Science 5 The Divergent Maze Runner, Science 4 Coach Ezzi Strikes Back, vocab for science chapter 3, Science 3 is this the real life, Science 2 electric boogaloo, Science Prologue

Satellite

A projectile or small celestial body that orbits a larger celestial body.

m1xm2/d^2

According to Newton, any body attracts any other body with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance separating them. This statement can be expressed as

the closed path taken by a point that moves in such a way that the sum of its distances from two fixed points (called foci) is constant

An ellipse is a specific curve:

less eccentric (more nearly circular

As muzzle velocity is increased, the ellipses are

continual free fall.

Astronauts in orbit are in a state of

space sickness

Astronauts in orbit are without a support force and are in a sustained state of weightlessness. They sometimes experience "_______________" until they become accustomed to a state of sustained weightlessness.

no horizontal force acts on the ball and its velocity is constant.

If the retarding effect of friction can be ignored

Impulse formula

Impulse=Force x time

escape velocity

In today's spacefaring age, it is more accurate to say, "What goes up may come down," for a critical starting speed exists that permits a projectile to escape Earth. This critical speed is called the escape speed or, if direction is involved,

a tiny segment of a skinny ellipse that extends within and just beyond the center of Earth

Interestingly enough, the parabolic path of a projectile, such as a tossed baseball or a cannonball, is actually a

The idea of matter is easy to grasp

Matter is stuff that we can see, smell, and feel. Matter has mass and occupies space.

you are as heavy as you feel

So a broader definition of the weight of something is the force it exerts against a supporting floor or a weighing scale. According to this definition,

Weight

The force that an object exerts on a supporting surface (or, if suspended, on a supporting string), which is often, but not always, due to the force of gravity.

gravity and for all phenomena in which the effect from a localized source spreads uniformly throughout the surrounding space

The inverse-square law holds for

Their combined effect produces the trajectories of projectiles.

When air resistance is small enough to ignore, the horizontal and vertical components of a projectile's velocity are completely independent of one another.

For example, a golf club that strikes a ball exerts zero force on the ball until it comes in contact; then the force increases rapidly as the ball is distorted (Figure 3.3). The force then diminishes as the ball comes up to speed and returns to its original shape. So when we speak of such forces in this chapter, we mean

average force

If the momentum of an object changes, then

either the mass or the velocity or both change.

Momentum is conserved for all collisions

elastic and ineleastic

Perhaps the concept most central to all of science

energy

When we consider the quantity force×distance, f⁢o⁢r⁢c⁢e×d⁢i⁢s⁢t⁢a⁢n⁢c⁢e, we are talking about something entirely different

energy

By hitting the haystack instead of the wall, you

extend the time during which your momentum is brought to zero

The forces involved in impulses usually vary from

instant to instant

a pair of 1

kg masses that are 1 m apart: 0.0000000000667 N.-The magnitude of G is identical to the magnitude of the force between

Formula for Momentum

momentum = mass x velocity

net momentum before collision=

net momentumafter collision

something else is important in changing momentum:

time

, force×distance◂⋅▸f⁢o⁢r⁢c⁢e×◂⋅▸d⁢i⁢s⁢t⁢a⁢n⁢c⁢e equals the concept we call

work.

The greater weight is more effective in ______________ air, resulting in a higher terminal speed for a heavier person. Increasing ____________ area reduces terminal speed.

"plowing through"; frontal

47.An airplane with an airspeed of 90 km/h lands on a runway where the wind speed is 40 km/h. What is the landing speed of the plane if the wind is head on? What is its landing speed if the wind is a tailwind, coming from behind the airplane? What would be the landing speed of the 90km/h plane landing in a headwind of 90 km/h?

-A. 50km.h B. 130km.h C. 0km/h

55.A ball is thrown straight up with enough speed so that it is in the air for several seconds. What is the velocity of the ball when it reaches its highest point? What is its velocity 1 s before it reaches its highest point? What is the change in its velocity, Δv, during this 1s interval? What is its velocity 1 s after it reaches its highest point? What is the change in its velocity, Δv, during this 1-s interval? What is the change in its velocity, Δv, during the 2-s interval from 1 s before it reaches the highest point to 1 s after it reaches the highest point? (Caution: We are talking about velocity, not speed.) What is the acceleration of the ball during any of these time intervals and at the moment the ball has zero velocity?

-A. Velocity at the highest point is instantaneously zero. B. One second before reaching its highest point, its velocity is 10 m/s. C. The amount of change in velocity is 10 m/s downward during this 1-second interval (or any other 1-second interval). D. One second after reaching its highest point its velocity is 10 m/s downward. E. The change in velocity during this (or any) 1-second interval is 10 m/s downward. F. The change in velocity, from 10 m/s up to 10 m/s down, is 20 m/s downward (not zero). G. The acceleration of the ball is 10 m/s2 downward before reaching its highest point, when reaching the highest point, and after reaching the highest point. In all cases acceleration is downward, toward Earth.

46.Driving along the road at 88 km/h, Reckless Rick runs into Hapless Harry, who is directly in front of him and is driving at 80 km/h. What is the impact speed—that is, the speed of the two vehicles the moment after collision?

0km/h

One watt (W) of power is used when

1 J of work is done in 1 s

52.A force F acts in the forward direction on a cart of mass m. A friction force f opposes this motion. Use Newton's second law and show that the acceleration of the cart is F−fm. Show that if the cart's mass is 4.0 kg, the applied force is 12.0 N, and the friction force is 6.0 N, the cart's acceleration is 1.5 m/s2.

1.5m/s/s=(12N-6N)/4kg

116.In the pulley system shown, Block A has a mass of 10 kg and is suspended precariously at rest. Assume that the pulleys and string are massless and there is no friction. No friction means that the tension in one part of the supporting string is the same as in any other part. Discuss why the mass of Block B is 20 kg.

10 kg- has one rope its pulling down on with 100 N (100N tension) wehich equals it out. Meanwhile, the 2nd block has two ropes holding it up, which gives htme a mechanical advantage of 200 N. Law of conservation of energy for machines. The law states that the input force times the input distance equals the output force time the output distance.

26.What is the efficiency of a machine that miraculously converts all the input energy to useful output energy?

100%

100.The orbital velocity of Earth about the Sun is 30 km/s. If Earth were suddenly stopped in its tracks, it would simply fall radially into the Sun. Devise a plan whereby a rocket loaded with radioactive wastes could be fired into the Sun for permanent disposal. How fast and in what direction with respect to Earth's orbit should the rocket be fired?

100. 41.2 km/s. This is because the escape velocity of Earth is 11.2 km/h so you can get it out of Earth and the 30km/s is the escape velocity of the sun. This will cause the waste to escape Earth and go faster than it to reach the sun and dispose of it so Earth doesn't burn up.

101.At what point in Earth's elliptical orbit about the Sun is the acceleration of Earth toward the Sun a maximum? At what point is it a minimum? Defend your answers.

100. 41.2 km/s. This is because the escape velocity of Earth is 11.2 km/h so you can get it out of Earth and the 30km/s is the escape velocity of the sun. This will cause the waste to escape Earth and go faster than it to reach the sun and dispose of it so Earth doesn't burn up.

102.The force of gravity on an Earth satellite in circular orbit remains constant at all points along the orbit. Why is this not the case for a satellite in an elliptical orbit?

102. IN a circular orbit, the satellite is the same distance away from the Earth throughout the entire orbit. According to the law of universal gravitation: F=G*(m1*m2)/d^2. This means that the force of gravitation on an object comes from its mass and distance, so if they both remain the same, they will have a constant force of gravity that doesn't change on them. For elliptical orbits, the orbit is oval shaped, and the planet is strictly on one side of it. This makes it to where the distance varies throughout the entire orbit, and back to the universal law of gravitation, if distance changes constantly, so will the gravitational attraction.

106.Comment on whether or not the following label on a consumer product should be cause for concern.CAUTION: The mass of this product pulls on every other mass in the universe, with an attracting force that is proportional to the product of the masses and inversely proportional to the square of the distance between them.

106. It should not because all bodies attract one another with an attracting force the strength of which is directly proportional to the product of their two masses divided by the squared distance between their centers. This force is so small that it is negligible most of the time.

108."Okay," a friend says, "gravitational force is proportional to mass. Is gravitation then stronger on a crumpled piece of aluminum foil than on an identical piece of foil that has not been crumpled? Isn't that why the crumpled one falls faster when they are dropped together?" Defend your answer and explain why the two fall differently.

108. No it is not, the reason the crumpled piece falls faster is because it has a smaller surface area/weight ration that itself before. This makes it fall faster. By lessening the surface area, more weight is added. This also applies to the sheet of aluminum foil, it has a big surface area, so hence it has less weight.

56.A school bus slows to a stop with an average acceleration of −2.0 m/s2. Show that it takes 5.0 s for the bus to slow from 10.0 m/s to a stop.

10m/s/2m/s/s=5s

110.Jupiter is more than 300 times as massive as Earth, so it might seem that a body on the surface of Jupiter would weigh 300 times as much as it would weigh on Earth. But it so happens that a body would weigh scarcely three times as much on the surface of Jupiter as it would on the surface of Earth. Discuss why this is so. (Hint: Let the terms in the equation for gravitational force guide your thinking.)

110. It is because of the equation for the universal law of gravitation. F=G(m1*m2)/d^2. This shows that gravitational attraction goes down as the squared distance between the two bodies' centers goes up. Sure, there may be an increase in mass, but that also means there shall be an increase in distance because mass is how much matter is in an object, so that means there needs to be more room for more mass.

112.Explain why the following reasoning is wrong. "The Sun attracts all bodies on Earth. At midnight, when the Sun is directly below, it pulls on you in the same direction as Earth pulls on you; at noon, when the Sun is directly overhead, it pulls on you in a direction opposite to Earth's pull on you. Therefore, you should be somewhat heavier at midnight and somewhat lighter at noon."

112. The Sun does not pull on you in the same direction the Earth does. The sun pulls on you out of the Earth and into it in all directions, while the Earth pulls you into it in all directions. If we were to draw a circular orbit for Earth's gravitation and an elliptical orbit for the sun's gravitation, you would notice that if anything, their gravities are in opposite directions unless you are in a specific spot at a specific time, and even then, that merely just looks like the sun is helping. Depending on where you are standing depends on whether or not that will even happen. Also, the sun pulls on ALL bodies. That includes the Earth too, so the sun is not pulling you into Erath at all it is pulling you and Earth into it.

116.A park ranger shoots a monkey hanging from a branch of a tree with a tranquilizing dart. The ranger aims directly at the monkey, not realizing that the dart will follow a parabolic path and thus will fall below the monkey. The monkey, however, sees the dart leave the gun and lets go of the branch to avoid being hit. Will the monkey be hit anyway? Does the velocity of the dart affect your answer, assuming that it is great enough to travel the horizontal distance to the tree before hitting the ground? Defend your answer.

116. The monkey will still get hit by the dart because he is falling straight into it, but only if the speed of the dart is quick enough. Speed of the dart does matter. If it travels too slow, it will not make it in time, and if it travels too fast, it won't hit the monkey, but most likely in the end it will. The monkey is falling down and so is the dart. Since the dart was aimed at where the monkey was and the monkey lets go when it sees the dart shootout, the two objects will be falling down at the same rate.

120.A friend says that astronauts inside the International Space Station (ISS) are weightless because they're beyond the pull of Earth's gravity. Correct your friend's reasoning.

120. Everything's gravitational attraction extends forever, it approaches zero but it never arrives at it, so yes it does pull on it. The thing is though, Earth's attraction, in this case, is so low that the force of attraction is negligible and does not really affect the station at all. This is backed up by the fact that the formula for gravitational attraction is G(m1*m2)/d^2. The fact that distance is squared means for far away things like a satellite away from Earth is squared and then proceeded to be the divider of the product of their masses will produce an extremely small attraction force.

124.As part of their training before going into orbit, astronauts experience weightlessness when riding in an airplane that is flown along the same parabolic trajectory as a freely falling projectile. A classmate says that gravitational forces on everything inside the plane during this maneuver cancel to zero. Another classmate looks to you for confirmation. What is your response?

124. The gravitational forces don't cancel out to zero. They still act on you. When in free fall or even in space, weightlessness is under the influence of gravity only. Another word for weightlessness is free fall. The gravitational forces are still there but your support force isn't. Your feeling of weight comes from the support force pushing up on you, so when that support force is taken away, you feel like you're weightless.

130.Here's a situation to challenge you and your friends: A rocket coasts in an elliptical orbit around Earth. To attain the greatest amount of KE for escape using a given amount of fuel, should it fire its engines at the apogee (the point at which it is farthest from Earth) or at the perigee (the point at which it is closest to Earth)? (Hint: Let the formula Fd = ΔKE guide your thinking. Suppose the thrust F is brief and of the same duration in either case. Then consider the distance d that the rocket would travel during this brief burst at the apogee and at the perigee.)

130. They should fire up the engines at the apogee because when the reach that point and start going back down, the gravitational attraction will increase more and more because you are getting closer to the Earth, which in turn will give the rocket more and more velocity plus the already existing velocity from the engine, which in turn will give it more KE because if velocity doubles, KE quadruples.

Universities emerged in Europe in

13th century

Scientific thought was furthered in

16th century with the advent of the printing press.

96.Harry the painter swings year after year from his bosun's chair. His weight is 500 N, and the rope, unbeknownst to him, has a breaking point of 300 N. Why doesn't the rope break when he is supported as shown at the left? One day, Harry was painting near a flagpole, and for a change, he tied the free end of the rope to the flagpole instead of to his chair, as shown at the right. Discuss with your friends why Harry took his vacation early.

2 ropes being held= double strength. 1 rope being held= single strength.

73.Suppose the monkey weighs 100 N and the vine supporting her pulls upward with a force of 120 N. What is the net force on the monkey? Describe her motion.

20 N. her motion is that she is going upwards and something is pulling upwards on the vine. More than two forces are pulling upward. She will go upward until the force pulling her upward stops pulling or the force pulling her upwards is less than or equal to her own weight. The net force is 120 N − 100 N = 20 N, so the monkey accelerates upward while the force acts.

They also conflicted with Church teachings and were banned for

200 years

what happens when a fisher goes upstream with a 10m/s current boat gies at 27 mph compared to water. Compared to land

27m/s. 17m/s

44.A business jet of mass 30,000 kg takes off when the thrust for each of two engines is 30,000 N. Show that its acceleration is 2 m/s2.

2m/s/s=60000N/ 30000kg

7.If a ball has the same speed just before being caught and just after being thrown, in which case does the ball undergo the greatest change in momentum: (1) When it is caught, (2) when it is thrown, or (3) when it is caught and then thrown back?

3

8.In which of cases (1), (2), and (3) in Question 7 is the greatest impulse required?

3

43.The sketch shows a painter's scaffold in mechanical equilibrium. The person in the middle weighs 500 N, and the tension in each rope is 400 N. What is the weight of the scaffold?

300 N

48.(a) Show that the average speed of a tennis ball is 48 m/s when it travels the full length of the court, 24 m, in 0.5 s. (b) How would greater air resistance affect the travel time?

48m/s=24/0.5 Greater air resistance greater travel time

50.Suzie Skydiver with her parachute has a mass of 50 kg. Before opening her chute, what force of air resistance will she encounter when she reaches terminal velocity? What force of air resistance will she encounter when she reaches a lower terminal velocity after the chute is open? Discuss why your answers are the same or different.

5N, 5N, They are the same because when falling the downward force never changes. In this case, your mass never chanegs when falling

18.If a moving car speeds up until it is going three times as fast as it was, how much kinetic energy does it have compared with its initial kinetic energy?

6 times as much

62.What would be the path of the Moon if somehow all gravitational acting forces on it sank to zero?

62. It would move in a straight line for all eternity because the moon has tangential velocity. This velocity keeps the moon constantly moving in a straight line. The gravitational pull of the Earth on the moon though, makes the moon orbit around the Earth, so if those gravitational forces were to cease to exist, all that would be left would be the moon's tangential velocity which will keep it in a straight line as mentioned before. It will stay like this because of inertia which is an object's tendency to resist changes in motion. Chances are, it could orbit another planet but if other planets and all gravity in general is negligible then the moons are gonna move until something stops it.

64.Consider a space pod somewhere between Earth and the Moon, at just the right distance so that gravitational attraction to Earth and gravitational attraction to the Moon are equal. Is this location nearer Earth or nearer the Moon?

64. The pod would be closer to Earth because of the universal law of gravity. The law in equation form is G*(m1*m2)/d^2. This means that gravitational attraction is directly proportional to mass, which means that the more mass, the more gravitational attraction. In this case, the Earth obviously has way more mass, so that means that the product of it and the pod will be much bigger compared to that of the moon and the pod, so that means the pod will be attracted much more to the Earth than the Moon.

66.An astronaut lands on a planet that has the same mass as Earth and twice the diameter. How does the astronaut's weight differ from her or his weight on Earth?

66. The force of gravity of the planet is 4 times bigger than that of the Earth. This is because in the universal law of gravitation, the equation for it, G(m1*m2)/d^2, states that the squared distance of the object's distance from their centers is inversely proportional to the amount of gravitational attraction between them. In other words, the more distance, the less gravitational attraction. In this case scenario, with the diameter being twice as big as the Earth, the distance between the center of it and the astronaut's center is much bigger than that of the Earth, so if this information is plugged in with any arrangement of numbers as long as it follows the criteria, the product will always be four times as big as the Earth's.

68.How would the force between a planet and its moon change if its moon were boosted to twice its distance from the center of the planet? If it were instead brought to half its distance from the center of the planet?

68. The force between the planet and its moon would be 4 times less because of the universal law of gravity. The formula form for this equation is G(m1*m2)/d^2. This shows that distance squared is inversely proportional to gravitational attraction. This means that when the moon gets 2 times farther from the planet, the distance will increase and since in the formula, distance is squared, it would more than be like the distance being 4 times as much. Once the formula is filled out, the result will end in a gravitational attraction 4 times as less.

52.Extend Table 1.2 (which gives values from 0 to 5 s) from 6 s to 10 s, assuming no air resistance.

6s 60 m/s 140 m; 7s 70m/s 155m; 8s 80m/s 170 m; 9s 90m/s 185m; 10s 100m/s 200m

70.In 2013, Curiosity landed on the surface of Mars. Does the weight of Curiosity vary if it makes its way from a valley floor to the top of a tall hill? Explain.

70. It does because of the universal law of gravity. The formula form for this equation is G(m1*m2)/d^2. This shows that distance squared is inversely proportional to gravitational attraction. This means that the higher the distance the less gravitational attraction. This means that when she gets to the top of the hill, she will be farther away from mars's surface from when he was on the ground. This will make her attraction less but since the amount is very little, the attraction decrease is negligible, but if it were to go through the calculation process and be compared to the attraction to the ground, it will be less.

41.Lucy Lightfoot stands with one foot on one bathroom scale and her other foot on a second bathroom scale. Each scale reads 350 N. What is Lucy's weight?

700 N

76.In synchronized diving, divers remain in the air for the same time. With no air resistance, they would fall exactly together. But air resistance is appreciable, so how do they remain together in fall?

76. When in the air, the divers are in a state of weightlessness, so that means they are under the influence of gravity only. Gravity exerts the same amount of force on all objects: 9.8 N. This is backed up by the fact that the more force on an object, the more air resistance so it makes all objects accelerate the same amount. Since they are only guided by this factor of weightlessness, they fall at the same rate.

78.If you were in a freely falling elevator and you dropped a pencil, it would hover in front of you. Is there a force of gravity acting on the pencil? Defend your answer.

78. There is gravity still acting on the pencil because it is falling with you. As you both fall, you both enter a state of weightlessness because the support force that elevator was gotten rid of and now the elevator is falling. This means that you and the pencil are falling with each other. You are all going down because gravity is pushing you all down with a force of 9.8 N.

80.How does the size of Pluto compare with that of planets in the solar system?

80. It is much smaller than all the other planets which gives it a higher gravity than all of them. This is because if you were to stand on pluto, you would be closer to it's center, so there would be more gravitational attraction because of the formula for gravitational attraction G(m1*m2)/d^2. So as the distance goes down, the gravitational attraction goes up due to distance^2 being inversely proportional to gravitational attraction.

82.Earth and the Moon are gravitationally attracted to the Sun, but they don't crash into the Sun. A friend says that is because Earth and the Moon are beyond the Sun's main gravitational influence. Other friends look to you for a response. What is your response?

82. The friend is wrong. Firstly, gravitational attraction will approach 0 but it will never arrive at 0. This means you will always feel the gravitational pull of everything in the universe. The Earth and the moon will not crash into the moon because the tangential velocity of the planets. Basically, the planets are moving in a straight line forever because of inertia, and inertia is an object's tendency to resist change in motion. Now you have a rude outside force butting in and trying to pull the Earth with its own force. The Earth will then be resisting the two come to a compromise of Earth just going around in a circle of the sun

84.In the absence of air resistance, why does the horizontal component of a projectile's motion not change, while the vertical component does?

84. It is because gravity doesn't act horizontally. The motion changes vertically because when an object goes down, gravity pushes on it and accelerates it. When the object goes up, gravity pushes on it and decelerates it. When gravity goes left or right, nothing makes it keep going in a direction. The only reason it is even moving is because you put a force on it.

88.When you jump upward, your hang time is the time your feet are off the ground. Does hang time depend on the vertical component of your velocity when you jump, on your the horizontal component of your velocity, or on both? Defend your answer.

88. It depends on your vertical because neglecting air resistance, the horizontal motion undergoes no change in motion. Meanwhile, the vertical motion does undergo a change in motion. This means that when you jump, the higher you are up, the more change in motion has to be undergone to get you back to the ground, while the horizontal motion can't even do anything to get you higher or in the air for longer. They are also independent of each other, so hOrizontal can't add onto vertical's speed at all

98.When the strong man in Exercise 97 exerts a downward force of 900 N on the rope, how much upward force is exerted on the block?

900 Newtons because the man is pulling on the rope that holds the block so on his side, he is exerting a downward force of 900 N, but on the other side, he is causing an upward force of 900 N to lift the block. He may not leift it, but he still exerting a force on it.

94.Does the speed of a falling object depend on its mass? (Recall the answer to this question in earlier chapters.) Does the speed of a satellite in orbit depend on its mass? Defend your answers.

94. No because the amount of mass on an object equals the amount of force on it. Every time, this will equal to 10m/s/s. For example, 4 kg=40N so in the formula for NEwton's second law: f/m=acceleration, 40/4=10. The speed of a satellite in space does depend on its mass because the more mass, the more inertia, and thus the less speed on it or the more force needed to get it at a high speed. All objects must go at at least 11.2 km/s to break out of Earth's surface, this means that a high mass object needs a higher force to get it at that speed.

96.What is the shape of the orbit when the velocity of the satellite is everywhere perpendicular to the force of gravity?

96. The shape is circular because if the velocity is in a straight line while the circular Earth is pulling it down, it would be pulling it down on every point of it into one singular middle core. This would make the path bend into a circular shape. This can be backed up by tangential velocity, which is a velocity of an object orbiting Earth, it is a straight line and Earth pulls on it everywhere into a singular point, so it makes it circular.

98.How could an astronaut in a space vehicle "drop" an object vertically to Earth?

98. It could be dropped from a still vehicle above earth. This can be also backed up by the fact that the horizontal motion and vertical are independent to each other, so if a craft was already orbiting the Earth, the box will stay in that horizontal motion and be pulled by the vertical motion at the same time, or if a craft was above Earth and not orbiting it, it could drop the object straight down and only the vertical force would act on it since there would be not horizontal force acted on it.

59.The strong man is pulled in the three situations shown. Rank, from least to greatest, the amount of tension in the rope in his right hand (the one attached to the tree in B and C).

A = B, C

Elastic collision

A collision in which colliding objects rebound without lasting deformation or the generation of heat.

Inelastic collision

A collision in which the colliding objects become distorted, generate heat, and may even stick together.

Fuel cell

A device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent.

Machine

A device, such as a lever or pulley, that increases (or decreases) a force or simply changes the direction of a force.

Law

A general hypothesis or statement about the relationship of natural quantities that has been tested over and over again and has not been contradicted; also known as a principle.

fact

A phenomenon about which competent observers who have made a series of observations are in agreement.

vector quantity

A quantity whose description requires both magnitude and direction.

103.Earth is farthest away from the Sun in July and closest in January. In which of these two months is Earth moving faster around the Sun?

A satellite travels fastest when closest to the body it orbits. Therefore Earth travels faster about the Sun in January than in July.

Lever

A simple machine consisting of a rigid rod pivoted at a fixed point called the fulcrum.

Theory

A synthesis of a large body of information that encompasses well-tested and verified hypotheses about certain aspects of the natural world.

45.A horizontal force of 120 N is required to push a bookcase across a floor at a constant velocity. What is the net force acting on the bookcase How much is the friction force that acts on the sliding bookcase? How much friction force acts on the bookcase when it is at rest on a horizontal surface without being pushed?

A. 0N B. 120N C. 0N

54.A ball is thrown straight up with an initial speed of 30 m/s. How much time does it take for the ball to reach the top of its trajectory? Show that it will reach a height of 45 m (neglecting air resistance).

A. 2s B.30=45m/1.5s

49.(a) Show that Leslie's average speed is 10 km/h when she runs to the store 5 km away in 30 min. (b) How fast is this in units of m/s?

A. 5km/h/0.5h=10km/h B. 10km divided by h* 1h/3600s*1000m/1km=2.8m/s

50.(a) Show that the acceleration is 7.5 m/s2 for a ball that starts from rest, rolls down a ramp, and gains a speed of 30 m/s in 4 s. (b) Would its acceleration be greater or less if the ramp were a bit less steep?

A. 7.5m/s/s=30m/s/4s B. less

60.Different materials, A, B, C, and D, rest on a table. (a) Rank the materials, from greatest to least, by how much they resist being set into motion. (b) Rank the materials, from greatest to least, by how much support force (normal force) the table exerts on them.

A. B,A,C,D B. B,A,C,D

57.An airplane starting from rest at one end of a runway accelerates uniformly at 4.0 m/s2 for 15 s before takeoff. What is its takeoff speed? Show that the plane travels along the runway a distance of 450 m before takeoff.

A. From v = v0 + at, and with v0 being zero, v = at = (4.0 m/s2)(15 s) = 60 m/s. B. With v0 being 0, d = ½at2 = ½(4 m/s2) (15 s)2 = 450 m.

69.You hold an apple over your head. (a) Identify all the forces acting on the apple and their reaction forces. (b) When you drop the apple, identify all the forces acting on it as it falls, as well as the corresponding reaction forces.

A. Two force pairs act; Earth's pull on the apple (action), and the apple's pull on Earth (reaction). Hand pushes apple upward (action), and apple pushes hand downward (reaction). B. If air resistance can be neglected, one force pair acts; Earth's pull on apple, and apple's pull on Earth. If air resistance counts, then air pushes upward on apple (action) and apple pushes downward on air (reaction).

47.Leroy, who has a mass of 100 kg, is skateboarding at 9.0 m/s when he smacks into a brick wall and comes to a dead stop in 0.2 s. Show that his deceleration is 45 m/s2. Show that the force of impact is 4500 N. (Ouch!)

A. a=ΔvΔt=9.0 m/s/0.2 s=45 m/s2 B. F=ma=(100 kg)(45 m/s2)=4500 N

58.Three parachutists, A, B, and C, have reached terminal velocity at the same altitude. (a) Rank their terminal velocities from fastest to slowest. (b) Rank the order of their reaching the ground from longest time to shortest time.

A. c,a,b B. c,a,b

51.Lillian rides her bicycle along a straight road at an average velocity v. Write an equation showing the distance she travels in time t. If Lillian's average speed is 7.5 m/s for a time of 5.0 min, show that she travels a distance of 2250 m.

A. d=? From v=d/t d=vt B. First, we need a consistent set of units. Since speed is in m/s let's convert minutes to seconds: 5 min= 300s Then d=vt=(7.5m/s)(300s)=2250 m

103.In the absence of air resistance, a ballplayer tosses a ball straight up. (a) By how much does the speed of the ball decrease each second while it is ascending? (b) By how much does its speed increase each second while it is descending? (c) How does the time of ascent compare to the time of descent?

A. the ball slows by 10 m/s each second, and B. gains 10 m/s when descending. C. With no air resistance the time of ascent equals the time of descent.

53.A car races on a circular track of radius r. Write an equation for the car's average speed when it travels a complete lap in time t. The radius of the track is 400 m, and the time to complete a lap is 40 s. Show that the average speed around the track is about 63 m/s.

A. v=d/t=2(pi)r/t B. V=2(pi)r/t=2(pi)(400m)/40s=63m/s

formula for acceleration

A=change in velocity/ time interval

93.Consider a freely falling object dropped from rest. What is its acceleration at the end of 5 s? At the end of 10 s? Defend your answer (and distinguish between velocity and acceleration).

Acceleration is 10 m/s2 downward, constant, all the way down. (Velocity, however, is 50 m/s downward at 5 seconds, and 100 m/s downward at 10 seconds.)

89.What is the acceleration of a Tesla automobile that maintains a constant velocity of 150 km/h?

Acceleration is zero since there's no change in velocity.

There is a simple rule for identifying action and reaction force pairs. First, identify the interaction—one thing (object A) interacts with another (object B). Then, action and reaction forces can be stated in the following form:

Action: Object A exerts a force on object B. Reaction: Object B exerts a force on object A.

109.A couple of your friends say that before a falling body reaches terminal velocity, it gains speed while acceleration decreases. Do you agree or disagree with your friends? Defend your answer.

Agree with your friends. Although acceleration decreases, the body is nevertheless gaining speed. It will do so until it reaches terminal speed. Only then will it not continue gaining speed.

107.Can you think of a reason why the acceleration of the object thrown downward through the air in Exercise 106 would actually be less than 10 m/s2?

Air resistance on the thrown object decreases the net force on it (mg − R), making its acceleration less than that of free fall.

115.Why bother using a machine if it cannot multiply work input to achieve greater work output?

Although a machine cannot multiply energy, it can multiply force or multiply distance, both of which can be of value.

Vector

An arrow that represents the magnitude and direction of a quantity.

Hypothesis

An educated guess; a reasonable explanation of an observation or experimental result that is not fully accepted as factual until tested over and over again by experiment.

117.If an automobile had a 100% efficient engine, transferring all of the fuel's energy to work, would the engine be warm to your touch? Would its exhaust heat the surrounding air? Would it make any noise? Would it vibrate? Would any of its fuel go unused? Discuss.

An engine that is 100% efficient would not be warm to the touch, nor would its exhaust warm the air, nor would it make any noise, nor would it vibrate. This is because all these are transfers of energy, which cannot happen if all the energy given to the engine is transformed to useful work.

Projectile

Any object that moves through the air or through space under the influence of gravity.

To increase the momentum of an object

Apply the greatest force possible for as long as possible

Europeans thought like

Aristotle

62.Knowledge can be gained by philosophical logic, and also by experimentation. Which of these did Aristotle favor, and which did Galileo favor?

Aristotle preferred to use philosophical logic in his search for knowledge. He would use common knowledge and reasoning to develop theories on how the world works. Galileo, on the other hand, preferred experimentation. He would use tests to provide solid evidence for his claims, which would make his assumptions more accurate than somebody who uses reasoning, which is not something that can be tested multiple times over to see if anything contradicts it. Nobody used experimentation till Galileo. Used experimentation to verify it.

Aristotle life

Aristotle was the foremost philosopher, scientist, and educator of his time. Born in Greece, he was the son of a physician who personally served the king of Macedonia. At age 17, he entered the Academy of Plato, where he worked and studied for 20 years until Plato's death. He then became the tutor of young Alexander the Great. Eight years later, he formed his own school. Aristotle's aim was to systematize existing knowledge, just as Euclid had systematized geometry. Aristotle made critical observations; collected specimens; and gathered, summarized, and classified almost all of the existing knowledge of the physical world. His systematic approach became the method from which Western science later arose. After his death, his voluminous notebooks were preserved in caves near his home and were later sold to the library at Alexandria. Scholarly activity ceased in most of Europe through the Dark Ages, and the works of Aristotle were forgotten and lost in the scholarship that continued in the Byzantine and Islamic empires. Several of his texts were reintroduced to Europe during the 11th and 12th centuries and were translated into Latin. The Church, the dominant political and cultural force in Western Europe, at first prohibited the works of Aristotle and then accepted and incorporated them into Christian doctrine.

64.A bowling ball rolling along a lane gradually slows as it rolls. How would Aristotle probably interpret this observation? How would Galileo interpret it?

Aristotle would reason that an object can only keep moving if a force acts on it. If not, it would return to it's natural rest. Galileo would determine that an object doesn't necessarily need a force acting on it to keep it moving. It's inertia would keep it moving forever, but an opposing force called friction would slowly start to slow it down until it reaches an equilibrium, or it's resting point. Aristotle would say the ball has a nutral resting place and for it to keep moving, a force had to keep it moving. Galileo would say inertia would keep it moving forever, but it would be stopped by rolling and fluid friction.

100.The opening photo in this chapter shows a favorite demonstration of author Steve Hewitt lying on his back with a blacksmith's anvil placed on his chest. When assistant Will Maynez whacks the anvil with a strong sledgehammer blow, Hewitt is not injured. How is the physics here similar to that illustrated in Figure 1.8 (the girl with a stack of books on her head)?

As a force travels through an object, the object's inertia makes the force smaller and smaller. This is true because Newton's 1st law states that all objects will remain in their state of motion unless acted upon by an outside force. This proves that if the force of the hammer beggins to go through the items or the anvil to reach the person and hurt them, the objects begin to resist the new outside force because of their inertia and break down the force as it travels until the force is either gone or so little that it doesn't hurt you

81.Suppose two carts, one twice as massive as the other, fly apart when the compressed spring that joins them is released. How fast does the heavier cart roll compared with the lighter cart?

As in the preceding exercise, the force on each cart will be the same. But since the masses are different, the accelerations will differ. The twice-as-massive cart will undergo only half the acceleration of the less massive cart and will gain only half the speed.

111.When will the gravitational force between you and the Sun be greater: today at noon or tomorrow at midnight? Defend your answer.

At noon you're closer to the Sun, so gravitation by the Sun on you is greater. Tomorrow at midnight you're one Earth diameter farther from the Sun and gravitation is weaker.

101.When a ball is tossed straight up, it momentarily comes to a stop at the top of its path. Is it in equilibrium during this brief moment? Why or why not?

At the top of its path (and everywhere else along its path) the force of gravity acts to change the ball's motion. Even though it momentarily stops at the top, the net force on the ball is not zero and it therefore is not in equilibrium.

Does ball B roll faster along the lower part of track B than ball A rolls along the straighter track A?

B rolls faster because it gains speed going more downhill. A, on the other hand, gains only one boost while B gains two. This will be canceled out however when it reaches thedip going up since it is the same as the dip going down, but instead of boosting, it is slowing down.

74.You tell your friend that the acceleration of a skydiver decreases as falling progresses. What is your response when your friend asks if this means the skydiver is slowing down?

Because acceleration is decreasing doesn't mean an object is slowing down. If an object is moving at 10m/s/s and after the 1st second it is moving at 10m/s. Then, let's say the acceleration will change to 9m/s/s after the 1st second as well. Once the second second arrives, the object will be moving at 19m/s because it is still gaining momentum, but at a lower rate. Eventually the object will reach terminal velocity where the acceleration will be 0, but it will still be moving because it has gained all that speed from before the acceleration hit 0, but it is no longer gaining any new speed

64.Aristotle claimed that the speed of a falling object depends on its weight. We now know that all objects in free fall, whatever their weight, undergo the same rate of change in speed. Why does weight not affect acceleration?

Because of air resistance, if there is more weight on an object, it will accelerate, but as it accelerates, inertia or air resistance (depending on what is happening) will act on the object. The more weight that acts on an object, the more inertia/ air resistance, which means it will balance out any amount of weight. If one weighed 10 lbs and had 2m/s, it would fall at 10 m/s^2 because that is what gravity exerts on anything. If another object fell at 20 lbs and had 4 m/s it would just be like the first one, and if you divided these two equations, you would get the same answer. Basically NEwton's second law in equation form is net force dividedf by mass is accelration. In this case the net force is weight.

66.When a ball rolls down an incline, it gains speed because of gravity. When a ball rolls up an incline, it loses speed because of gravity. Why doesn't gravity play a role when it rolls on a horizontal surface?

Because the ball is at rest and gravity presses it down, which would cause it to move if it were on a slope. Since it is not, however, gravity is just pushing it down, not sideways. An outside force is acting on the object to move it. Gravity is simply just pushing down, while an outside force can push anywhere depending on what the force is. Support fprce acts on an object from the dirction the ground is. If it wall on level grounf, it would point up. If it was on slanted ground it would point in the direction the ground is facimg. Vector result. Even the slightest change can affect this.

73.How does the weight of a falling body compare with the air resistance it encounters just before it reaches terminal velocity? Just after it reaches terminal velocity?

Before reaching terminal velocity, weight is greater than air resistance. After reaching terminal velocity both weight and air resistance are of the same magnitude. Then the net force and acceleration are both zero.

Weightless

Being without a support force, as in free fall.

2.When a ball is hit with a given force, why does contact over a long time impart more speed to the ball than contact over a short time?

Bigger impulse

87.Two golfers each hit a ball at the same speed, but one hits it at 60° with the horizontal and the other at 30°. Which ball goes farther? Which hits the ground first? (Ignore air resistance.)

Both balls have the same range ( Figure 4.19). The ball with the initial projection angle of 30°, however, is in the air for a shorter time and hits the ground first.

109.Which, if either, has greater momentum: a 1 kg ball moving at 2 m/s or a 2 kg ball moving at 1 m/s? Which has greater kinetic energy?

Both have the same momentum, but the 1 kg ball, the faster one, has the greater KE.

83.When you are traveling in your car at highway speed, the momentum of a bug is suddenly changed as it splatters onto your windshield. Compared with the change in momentum of the bug, by how much does the momentum of your car change?

By Newton's 3rd law, the force on the bug is equal in magnitude and opposite in direction to the force on the car windshield. The rest is logic: Since the time of impact is the same for both, the amount of impulse is the same for both, which means they both undergo the same change in momentum. The change in momentum of the bug is evident because of its large change in speed. The same change in momentum of the considerably more massive car is not evident, for the change in speed is correspondingly very small. Nevertheless, the magnitude of mΔV for the bug is equal to MΔv for the car!

59.Rank, from greatest to least, the net force on the block in the four situations, A, B, C, and D.

C,A,B,D

58.The weights of Burl, Paul, and the scaffold produce tensions in the supporting ropes. Rank, from greatest to least, the tension in the left rope in the three situations, A, B, and C.

C,B,A

17.Two cars are raised to the same elevation on service station lifts. If one car is twice as massive as the other, how do their potential energies compare?

Car with double the mass of the other 20 times more potential energy than the other

125.Would the speed of a satellite in close circular orbit about Jupiter be greater than, equal to, or less than 8 km/s?

Consider "Newton's cannon" fired from a tall mountain on Jupiter. To match the wider curvature of much larger Jupiter, and to contend with Jupiter's greater gravitational pull, the cannonball would have to be fired significantly faster. (Orbital speed about Jupiter is about 5 times that for Earth.)

One of the arguments against a moving Earth was the following:

Consider a bird sitting at rest on a branch of a tall tree. On the ground below is a fat, juicy worm. The bird sees the worm and drops vertically below and catches it. It was argued that this would be impossible if Earth were moving. A moving Earth would have to travel at an enormous speed to circle the Sun in one year. While the bird would be in the air descending from its branch to the ground below, the worm would be swept far away along with the moving Earth. It seemed that catching a worm on a moving Earth would be an impossible task. The fact that birds do catch worms from tree branches seemed to be clear evidence that Earth must be at rest.

81.In order to slide a heavy cabinet across the floor at constant speed, once it is sliding you exert a horizontal force of 550 N. Is the force of friction between the cabinet and the floor greater than, less than, or equal to 550 N? What happens to the cabinet if your push exceeds 550 N? Defend your answer.

Constant speed implies the net force on the cabinet is zero. So friction is 550 N in the opposite direction. If you push harder, the carton speeds up because your force is greater than the force of friction.

91.Correct your friend who says, "Japan's bullet trains can easily round a curve at a constant velocity of 160 km/h."

Constant velocity means constant direction, so your friend should say "... at a constant speed of 160 km/h."

77.Why are today's autos designed to crumple upon impact?

Crumpling allows more time for reducing the momentum of the car, resulting in a smaller force of impact on the occupants.

Formula for force of gravity directly and inversely proprotional

D: Mass I: D^2

formula for hang time

D=1/2*G*T^2

In the final days of his life, at the urging of close friends, Copernicus sent his manuscript, _______________,** to the printer.

De Revolutionibus Orbium Coelestium

Speed

Distance traveled per unit time.

102.Suppose that a freely falling object falls from a rest position and is equipped with an odometer. What equation is most appropriate for determining the distance fallen each second?

Do the readings indicate equal or unequal distances of fall for successive seconds? Explain. D=1/2*G*T^2 (formula for free fall) because the object is falling and we are trying to find the distance fallen each second. We would plug in 1 for T and plug in the other numbers and that would give us our answer.

71.Earth is not exactly a sphere but, rather, bulges outward at the equator. How does this bulge affect the relationship between a person's weight in Singapore and his or her weight in Hong Kong?

Due to the bulge a person in Singapore is farther from the Earth's center and therefore weighs less there. The spin of the Earth contributes to even less weight in equatorial regions, although in practice these effects are minuscule.

Equilibrium rule

EF=0

77.Nellie Newton hangs at rest from the ends of the rope as shown. How does the reading on the scale compare with her weight?

Each scale shows half her weight.

Physics and chemistry, applied to Earth and its processes, make

Earth science— geology, meteorology, and oceanography.

87.Emily Easygo can paddle a canoe in still water at 8 km/h. How successful will she be at canoeing upstream in a river that flows at 8 km/h?

Emily will not be successful, for her speed will be zero relative to the land.

Conservation of energy

Energy cannot be created or destroyed; it may be transformed from one form into another, but the total amount of energy never changes.

Kinetic energy

Energy of motion, quantified by the relationship

Scientific advance came to a near halt in

Europe when the Roman Empire fell in the 5th century ad.

Law of universal gravitation

Every body in the universe attracts every other body with a force the strength of which is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers

mass and distance

Everything pulls on everything else in a beautifully simple way that involves only

49.The heavyweight boxing champion of the world punches a sheet of paper in midair, bringing it from rest up to a speed of 25.0 m/s in 0.050 s. The mass of the paper is 0.003 kg. Show that the force of the punch on the paper is only 1.5 N.

F=ma=m×Δv/Δt=0.003 kg×25.0 m/s/0.050 s=1.5 N

free fall

Falling under the influence of gravity alone— falling without air resistance.

45.A rocket of mass 100,000 kg undergoes an acceleration of 2 m/s2. Show that the net force acting on it is 200,000 N.

Fnet=ma=(100,000 kg)(2 m/s2)=200,000 N

what do science and religion have in common

For example, both are motivated by curiosity for the natural. Both have great impact on society. Science, for example, leads to useful technological innovations, and religion provides a foothold for many social services. Science and religion, however, are basically different. Science is concerned with understanding the physical universe, while many religions are concerned with faith in, and the worship of, a supreme being and with the creation of human community—not the practice of science. While scientific truth is a matter of public scrutiny, religion is a deeply personal matter.

73.The intensity of light from a central source varies inversely as the square of the distance. If you lived on a planet only half as far from the Sun as our Earth, how would the light intensity compare with that on Earth? How about a planet five times as far away as Earth?

For the planet half as far from the Sun, light would be four times as intense. For the planet five times as far, light would be 1/25th as intense.

zero. The force approaches zero, but it never gets there. Even if you were transported to the far reaches of the universe, the gravitational influence of home would still be with you. It may be overwhelmed by the gravitational influences of nearer and/or more massive bodies, but it is there. The gravitational influence of every material object, however small or however far, is exerted through all of space.

For very great distances, Earth's gravitational force approaches

The action force and the reaction force that occur in an interaction.

Force pair

formula for force

Force=Mass*Acceleration

Motion under the influence of gravitational pull only.

Free fall

83.In Figure 1.15 we see Marie pushing horizontally on a table that slides across the floor at constant velocity. If she pushed with the same amount of force, but directed that force downward a bit, how would the amount of friction of the table legs with the floor be affected? Defend your answer.

Friction would be greater. With a somewhat downward push, the table would press harder against the floor (as if it were heavier). More friction acts on a sliding heavy table than on a lighter one.

137.A red ball of mass m and a blue ball of mass 2m have the same kinetic energy. Explain which of the two has the larger momentum, letting equations guide your discussion.

From KE = ½mv2, v = √(2KE/m). The red ball has momentum m√(2KE/m) = √(2KEm) and the blue ball has momentum 2m√(2KE/2m) = 2m√(KE/m) = √(4KEm). We see that blue ball's √(4KEm) > red ball's √(2KEm). The blue ball has the larger momentum, √2 times as much momentum as the red ball. Or without equations, the red ball with ½ the mass of the blue ball must move √2 as fast to have the same KE, which means its v2 is twice as large. Then its momentum is (½)(√2) = √2 times less than that of the blue ball.

formula for relationship between impulse and momentum

Ft=change in momentum

the universal gravitational constant.

G is called

90.If you've had the good fortune to witness the launching of an Earth satellite, you may have noticed that the rocket starts vertically upward, then departs from a vertical course and continues its climb at an angle. Why does it start vertically? Why does it not continue vertically?

GET CONFUSION CLEARED UP FIRST

92.Satellites are normally sent into orbit by firing them in an easterly direction, the direction in which Earth spins. What is the advantage of this?

GET PROBLEM FIXED FIRST

Italian scientist who was arrested for popularizing the Copernican theory and for his other contributions to scientific thought.

Galileo Galilei

Galileo life

Galileo was born in Pisa, Italy, in the same year Shakespeare was born and Michelangelo died. He studied medicine at the University of Pisa and then changed to mathematics. He developed an early interest in motion and was soon at odds with others around him, who held to Aristotelian ideas on falling bodies. He left Pisa to teach at the University of Padua and became an advocate of the new theory of the solar system advanced by the Polish astronomer Copernicus. Galileo was one of the first to build a telescope, and the first to direct it to the nighttime sky and discover mountains on the Moon and the moons of Jupiter. Because he published his findings in Italian instead of in Latin, which was expected of so reputable a scholar, and because of the recent invention of the printing press, his ideas reached many people. He soon ran afoul of the Church and was warned not to teach and not to hold to Copernican views. He restrained himself publicly for nearly 15 years. Then he defiantly published his observations and conclusions, which were counter to Church doctrine. The outcome was a trial in which he was found guilty, and he was forced to renounce his discoveries. By then an old man broken in health and spirit, he was sentenced to perpetual house arrest. Nevertheless, he completed his studies on motion, and his writings were smuggled out of Italy and published in Holland. His eyes had been damaged earlier by viewing the Sun through a telescope, which led to blindness at age 74. He died four years later.

120.What is the argument that dryrock geothermal power is a form of nuclear power?-

Geothermal comes from energy in the earth which comes from radioactive energy used top make the earth

69.Phil works on the 15th floor of an office building, and his wife Jean works on the 30th floor, which is twice as high as Phil's workplace. Is the force of gravity half as much in Jean's workspace as in Phil's? Explain why or why not.

Gravitational force is measured with respect to distance from Earth's center. Since the workplaces are practically the same distance from Earth's center any difference due to gravity is negligible.

formula for gravtational potential energy

Gravitational potential energy=weight×height

downward

Gravity acts only downward, so the only acceleration of the ball is

91.Newton knew that if a cannonball were fired from a tall mountain, gravity would change its speed all along its trajectory (Figure 4.29). But if it is fired fast enough to attain circular orbit, gravity does not change its speed at all. Explain.

Gravity changes the speed of a cannonball when the cannonball moves in the direction of Earth gravity. At low speeds, the cannonball curves downward and gains speed because there is a component of the force of gravity along its direction of motion. Fired fast enough, however, the curvature matches the curvature of the Earth so the cannonball moves at right angles to the force of gravity. With no component of force along its direction of motion, its speed remains constant.

inverse square law, as do the effects of electric, light, sound, and radiation phenomena.

Gravity follows an

Science made great headway in

Greece in the 3rd and 4th century BC

132.What are the roles of water, energy, hydrogen, and oxygen in (a) electrolysis, (b) operation of a fuel cell?

H2O is another way of saying water. Water splits into it's two compponenets: oxygen and hydrogen. Oxygen and hydrogen split apart from H2O into their separate components. Energy uses electric energy and kinetic energy to split water up into it's components. Energy and Oxygen combine to make H2O. Water is turned into electricity. Energy acts as kinetic energy to convert the water into electric energy, and it acts to combine oxygen and hydrogen to make water.

93.Hawaii presents the most efficient launching site in the United States for nonpolar satellites. Why is this so? (Hint: Look at the spinning Earth from above either pole, and compare it to a spinning turntable.)

Hawaii is closer to the equator, and therefore has a greater tangential speed about the polar axis. This speed could be added to the launch speed of a satellite and thereby save fuel.

86.A fully dressed person is at rest in the middle of a pond on perfectly frictionless ice and must get to shore. How can this be accomplished? Explain in terms of momentum conservation.

He could take off his clothes and throw them in front of him one at a time. According to the law of conservation of momentum, the momentum of a system that does not have an outside force acting on it remains unchanged. This means that when you throw your clothes, it's momentum activates and your momentum activates in the opposite direction, so if you were to keep throwing your clothes, they would go forward from the force exerted on them by you and their momentum with be going, and they would be exerting an opposite force on you and you would be going in the opposite direction.

90.The photo shows Steve Hewitt and his daughter Gretchen. Is Gretchen touching her dad, or is he touching her? Explain.

He is touching her and she is touching him. This is true because Newton's 3rd law states that for every action, there is an equal and opposite reaction. If Steve is touching his daughter as an action, then the reaction is that his daughter is touching him as well, or if his daughter is touching him, his reaction is that he is touching his daughter. If that doesn't prove it then this will: they are both literally touching each other with their hands. Steve has grabbed his daughters arms and his daughter has grabbed his arms. They are both sending actions to each other and receiving reactions from each other.

it would follow if there were no forces acting on it.

He realized that the Moon falls in the sense that it falls away from the straight line

100.A physics instructor demonstrates energy conservation by releasing a heavy pendulum bob, as shown, allowing it to swing to and fro. What would happen if, in his exuberance, he gave the bob a slight shove as it left his nose? Explain.

He will transfer some potential energy from his nose onto the bob, It will then turn into kinetic energy and give the bob a bigger boost. This is because of the law of conservation of energy. All energy is created nor destroyed. Instead, it is transferred and undergoes change. In this case scenario, the potential energy form your nose it transferred from your nose into the bowling ball and undergoes change into kinetic energy

77.Why can a boxer hit a heavy opponent harder for the same punch than she or he can hit a light opponent?

Hitting involves an interaction between the hitter and the hit. A boxer cannot hit an opponent harder than the opponent can 'hit' back. The amount of hitting force is greater in the interaction between a boxer and a heavy opponent than with a lighter one, just as a punch delivers more force to a heavy bag than to a piece of tissue paper

92.The auto in the sketch moves forward as the brakes are applied. A bystander says that during the braking interval, the auto's velocity and acceleration are in opposite directions. Do you agree or disagree?

I agree because when you step on the breaks, you decelerate the vehicle. You make the acccelration go into the negatives and it slows the car down to a stop, or it goes to an opposite direction and acclerates from there which decreases the speed going the other way

103.If a golf ball and a Ping Pong ball both move with the same kinetic energy, can you say which has the greater speed? Explain in terms of the definition of KE. Similarly, in a gaseous mixture of heavy molecules and light molecules with the same average KE, can you say which have the greater speed?

If KEs are the same but masses differ, then the ball with the smaller mass has the greater speed. That is, ½Mv2 = ½mV2. Likewise with molecules, where lighter ones move faster on the average than more massive ones. (We will see in Chapter 6 that temperature is a measure of average molecular KE—lighter molecules in a gas move faster than same temperature heavier molecules.)

5.Why is it advantageous, in karate, to apply a force for a short time?

If momentum occurs over a short period of time the force is large

85.If you throw a ball horizontally while standing on a skateboard, you roll backward with a momentum that matches that of the ball. Will you roll backward if you hold on to the ball while going through the motions of throwing it? Explain in terms of momentum conservation.

If no momentum is imparted to the ball, no oppositely directed momentum will be imparted to the thrower. Going through the motions of throwing has no net effect. If at the beginning of the throw you begin recoiling backward, at the end of the throw when you stop the motion of your arm and hold onto the ball, you stop moving too. Your position may change a little, but you end up at rest. No momentum given to the ball means no recoil momentum gained by you.

75.Can an object be in mechanical equilibrium when only a single force acts on it? Defend your answer.

If only a single nonzero force acts on an object, its motion will change and will not be in mechanical equilibrium. There would have to be other forces to result in a zero net force for equilibrium.

127.Will your answer to Question 126 be different if the air is brought to a halt by the sail without bouncing? Discuss.

If the air is brought to a halt by the sail without bouncing, then the impulse against the sail will be equal and opposite to the impulse on the fan. There will be no net impulse and no change in momentum. The boat will remain motionless. Bouncing matters!

117.The bricks in this road were originally straight. Describe evidence for tires pushing the bricks in the wavy pattern, and explain why they do so.

If the tires didn't push on the road the bricks would still be straight. Where the bricks fold toward the left, tires have pushed in that direction. Where the bricks fold to the right, tires have pushed in that direction. Tires push when the car accelerates forward, gaining speed, and in the opposite direction when tires push backward as the cars brake.

When do action and reaction forces cancel each other

If these are the only horizontal forces, with no external force, no net acceleration of the system occurs.

85.What is the impact speed when a car moving at 100 km/h collides with the rear of another car traveling in the same direction at 98 km/h? What is the impact speed when they collide head on?

Impact speed is 100 km/h − 98 km/h = 2 km/h, a small bump. Head on is 100 km/h + 98 km/h = 198 km/h, lethal!

97.Compared with a pickup truck moving at a certain speed and braking to a stop, how much work must the brakes do to stop the truck when it is moving at twice that speed?

In accord with W=ΔKE, twice the speed means four times the KE, so the brakes will have to do four times as much work.

89.When vertically falling sand lands in a horizontally moving cart, the cart slows. Ignore any friction between the cart and the tracks. Give two reasons for the slowing of the cart, one in terms of a horizontal force acting on the cart, and one in terms of momentum conservation.

In terms of force: When the sand lands on the cart it is brought up to the cart's speed. This means a horizontal force provided by the cart acts on the sand. By action reaction, the sand exerts a force on the cart in the opposite direction—which slows the cart. In terms of momentum conservation: Since no external forces act in the horizontal direction, the momentum after the cart catches sand equals the momentum before. Since mass is added, velocity must decrease.

Law of conservation of momentum

In the absence of an external force, the momentum of a system remains unchanged. Hence, the momentum before an event involving only internal forces is equal to the momentum after the event:

what do science and art have in common

In the art of literature, we find out about what is possible in human experience. We can learn about emotions such as rage and love, even if we haven't yet experienced them. The arts describe these experiences and suggest what may be possible for us. Similarly, a knowledge of science tells us what is possible in nature. Scientific knowledge helps us predict possibilities in nature even before we experience them. It provides us with a way of connecting things, of seeing relationships between and among them, and of making sense of the great variety of natural events around us.

119.To combat wasteful habits, we often speak of "conserving energy" by turning off lights, heating or cooling systems, and hot water when these are not being used. In this chapter, we also speak of "energy conservation." Distinguish between these two uses of the term conservation.

In the popular sense, conserving energy means not wasting energy. In the physics sense energy conservation refers to a law of nature that underlies natural processes. Although energy can be wasted (which means transforming it from a more useful to a less useful form), it cannot be destroyed—nor can it be created. Energy is transferred or transformed, without gain or loss. In short, that's what a physicist means in saying energy is conserved.

6.In boxing, why is it advantageous to roll with the punch?

Increases the time of impulse so the force gets smaller

Momentum

Inertia in motion, given by the product of the mass of an object and its velocity.

138.No work is done by gravity on a bowling ball resting or moving on a bowling alley, because the force of gravity on the ball acts perpendicular to the surface. But on an incline, the force of gravity has a vector component parallel to the alley, as sketch b shows. Discuss two ways in which this component (a) accounts for acceleration of the ball, and (b) accounts for work done on the ball to change its kinetic energy.

Inertia keeps the ball still and gravity does nothing to affect it. When leaning gravity does do domething to affect it

Mutual action between objects during which each object exerts an equal and opposite force on the other.

Interaction

Greek science was reintroduced to Europe by

Islamic influences that penetrated into Spain during the 10th, 11th, and 12th centuries.

23.An apple hanging from a limb has potential energy because of its height. If the apple falls, what becomes of this energy just before the apple hits the ground? When it hits the ground?

It becomes kinetic energy that has as much as the potential energy from before. It becomes potential energy but at a lesser amount from before, sound, vibrational, etc

82.Consider your desk at rest on your bedroom floor. As you and your friend start to lift it, does the support force on the desk provided by the floor increase, decrease, or remain unchanged? What happens to the support force on the feet of you and your friend?

It becomes less because you are helping the support force, so it decreases it's power because it only exists to equal out gravity and as you lift the desk it slowly turns to 0 when it is lifted because yu have equalled the support force and surpassed it, causing you to lift the table.

4.Why is it poor judgment to have the back of your hand up against the outfield wall when you catch a long fly ball?

It decreases the time of impulse and causes the momentum to decrease very fast and give all of it's force and inertia for it on your hand. Unlike 3, you don't have anything behind you to cushion it.

98.When a cannon with a long barrel is fired, the force of expanding gases acts on the cannonball for a long distance. What effect does this have on the velocity of the emerging cannonball? (Do you see why long range cannons have such long barrels?)

It increases the velocity of the bullet because the longer barre keeps the cannonball in the cannon for a longer time, which gives the gases more time to act on it, thus giving it a bigger time of impulse. When this happens, the cannonball will have a higher tiem in which forces will act on it, which will give it a higher momentum. Momentum is inertia in motion, and inertia is an object's tendency to resist change in motion. This will keep the cannonball moving for a longer amount of time.

78.A hockey puck at rest is in equilibrium. Is it in equilibrium if it slides across ice at constant velocity? Defend your answer.

It is because an object is the vector sum of forces acting on an object (in this case, friction and an outside force) and is not accelerating equals zero. A constant speed is a speed that doesn't change or accelerate, so that means the vector sum is zero. When a vector sum equals zero, that means it is in equilibrium, so in this case it is in a type of equilibrium called dynamic equilibrium in which an object that is in a constant speed is in equilibrium.

104.In the absence of air resistance, a snowball thrown vertically upward with a certain initial KE returns to its original level with the same KE. When air resistance is a factor affecting the snowball, does it return to its original level with the same, less, or more KE? Does your answer contradict the law of energy conservation?

It returns with the less than the starting amount of kinetic energy as before and it does not contradict the law of conservation of momentum. The law states that all energy is not created nor destroyed, it is transferred and undergoes change. In this case, the snowball goes up and the kinetic energy slowly changes into potential energy until it is all potential energy. Other energy turns into sund enrgy and goes everywhere, and other energy turns into thermal energy and vibrational energy and goes away from the huge group of energy. Once the rest fullly turns into kinetic energy, it stops at its highest point. It will then start to change back into kinetic energy and go down. It doesn't contradict the law because it didn't create any new energy or get rid of any of it, it just changed into different forms of it.

On track B, won't the average speed dipping down and up be greater than the average speed of ball A during the same time?

It will be dipping down, but dipping backup will make the average speed of B the same as A. This is because since they are both the same height, B will lose as much as it gained, so the boost and deboost will cancel each other out.

84.When the athlete holds the barbell overhead, the reaction force is the weight of the barbell on his hand. How is this force different when the barbell is lifted at an increasing speed?

It will only occur whe he begins to lift it and when he begins to slow down when he gets close to finishing lifting it in the air. WHen he begins or ends the weight's inertia will kick in and reists the change of motion. Atthe beginning it will exert mroe force to stop from being lifted or changed in it's form of mpotion andit will exert force to resist it being stopped or its motion being chaneghd again becaus eof NEwton's 1st law.

108.You throw a ball straight upward. Compared with its initial speed when thrown, how fast does it return to its starting point? Answer this for the case of no air resistance, and for the case where air resistance does affect motion.

It will return with the same amount of speed as the initial speed because when the object is thrown in the air, it will begin to start losing it's speed, and once it's speed arrives at 0, it will be at its highest point. It will then start gaining all that speed back on the way down because it took all that speed to get it up there and it began to lose that speed, so now, since it began to lose that speed per every second, it will also gain that speed per every second on the way down like counting down from 10 it would be like this with 0 being the highest point an d the negatives being the way down 10m/s, 9m/s, 8m/s, 7m/s, 6m/s, 5m/s, 4m/s, 3m/s, 2m/s, 1m/s, 0m/s, -1m/s, -2m/s, -3m/s, -4m/s, etc.

95.If a space vehicle circled Earth at a distance equal to the Earth-Moon distance, how long would it take for it to make a complete orbit? In other words, what would be its period?

It would be in a Moon orbit. Its period would be the same as the Moon's, 28 days.

105.An object tossed vertically will reach a maximum height. An object dropped from that same height would land with the same speed at which the first object was thrown. How fast would an object hit Earth if it were dropped from a distance beyond Neptune, falling only because of Earth gravity?

It would fall and hit at a speed of 11.2 km/s, Earth's escape speed.

92.Suppose that a freely falling object were somehow equipped with a speedometer. By how much would its speed readings increase with each second of fall?

It would move at 10 meters per second squared. This is because all objects in the same vicinity on Earth that are in freefall have the same acceleration which is 10 meters per second squared. An object near Earth's surface will gain an acceleration of 10 m/s, so the speedometer would increase by 10 m/s for every second of freefall.

65.A space probe is carried by a rocket into outer space. A friend wonders what keeps the probe moving after the rocket no longer pushes it. What do you say?

It's inertia will keep it moving forever because on Earth, inertia would keep objects moving forever but it would be stopped by outside forces, friction, gravity, weight etc. In space, however, there is no gravity/weight or anything else. therefore, the object will just keep moving forever until some other force acts on it like a gravitational pull or a meteor hitting it. You say that the probe keeps moving because no force acts to slow it. The probe moves of its own inertia. Changes in motion require a force; no force, no change.

108.When the velocity of an object is doubled, by what factor is its momentum changed? By what factor is its kinetic energy changed?

It's momentum increases 2 times as much as the velocity. This is because momentum is always incrased as much as the amount of velocity of something is increased. In this case, the velocity is doubled, so the momentum will be doubled.. It's kinetic energy is quadrupled as much as the velocity because the work energy theorem states that the total velocity= the change in kinetic energy.

110.If an object's kinetic energy is zero, what is its momentum?

It's momentum is 0 because momentum is inertia in motion. Kinetic energy is motion itself. Without kinetic energy, you've got no motion, so momentum can't happen. Also in order to have 0 KE you have to have 0 velocity

75.A lunar vehicle is tested on Earth at a speed of 12 km/h. When it travels at that same speed on the Moon, is its momentum more, less, or the same?

Its momentum is the same (its weight might change, but not its mass).

gravitational force with mass and distance.

Just as π relates circumference and diameter for circles, G relates

111.How does the gravitational force on a falling body compare with the air resistance it encounters before it reaches terminal velocity? After it reaches terminal velocity?

Just before a falling body attains terminal velocity, there is still a downward acceleration because gravitational force is still greater than air resistance. When the air resistance builds up to equal the gravitational force, terminal velocity is reached. Then air resistance is equal and opposite to gravitational force.

formula for kinetic energy

Kinetic energy=1/2 mass×speed^2

The 15th century saw art and science beautifully blended by

Leonardo da Vinci.

105.A rocket becomes progressively easier to accelerate as it travels through space. Why? (Hint: About 90% of the mass of a newly launched rocket is fuel.)

Let Newton's second law guide the answer to this; a=F/m. As m gets less (much the mass of the fuel), acceleration a increases while force remains constant.

65.An astronaut lands on a planet that has the same mass as Earth but half the diameter. How does the astronaut's weight differ from that on Earth?

Letting the equation for gravitation guide your thinking, half the diameter is half the radius, which corresponds to 4 times as much weight as on Earth.

Momentum and kinetic energy are properties of moving things, but they differ from each other.

Like velocity, momentum is a vector quantity and is therefore directional and capable of being canceled entirely. But kinetic energy is a nonvector (scalar) quantity, like mass, and can never be canceled.Energies transform to other forms; momenta do not. Another difference is the velocity dependence of the two. Whereas momentum depends on velocity (mv), kinetic energy depends on the square of velocity (12mv2).(◂⋅▸12⁢m⁢v2). An object that moves with twice the velocity of another object of the same mass has twice the momentum but four times the kinetic energy.

67.What physical quantity is a measure of how much inertia an object has?

Mass

69.Is a person on a diet more accurately said to lose mass or to lose weight? Defend your answer.

Mass, because mass is the amount of matter in something, and you are trying to lose your fat, or lose matter. Weight, on the other hand is the force of gravity on an object. You can't change gravity by going on a diet. A person on a diet loses mass. To lose only weight, the person could go to the top of a mountain where gravity is less. But the amount of matter would be the same.

85.At what point in its trajectory does a batted baseball have its minimum speed? If air resistance can be neglected, how does this compare with the horizontal component of its velocity at other points?

Minimum speed occurs at the top, which is the same as the horizontal component of velocity anywhere along the path.

112.Two lumps of clay with equal and opposite momenta have a head on collision and come to rest. Is momentum conserved? Is kinetic energy conserved? Why are your answers the same (or different)?

Momentum is conserved because it all changes abck into still inertia. Law of consrrvation of momentum. In this case, momentum is not created or destroyed, it just changes. Kinetic energy is not conserved. A bunch of it turns to entropy. Energy is conserved, but KE is not.

125.Your friend says that the law of momentum conservation is violated when a ball rolls down a hill and gains momentum. Your friend wants to discuss this. What do you say?

Momentum is not conserved for the ball itself because an impulse is exerted on it (a component of gravitational force × time). So the ball gains momentum. It is in the absence of an external force that momentum doesn't change. Whether momentum is conserved relates to the system involved. If the whole Earth and the rolling ball are taken together as a system, then the gravitational interaction between Earth and the ball are internal forces and no external impulse acts. Then the momentum of the ball is accompanied by an equal and opposite momentum change of Earth, which results in no change in momentum.

93.Which requires more work: stretching a strong spring a certain distance or stretching a weak spring the same distance? Defend your answer.

More force is required to stretch the strong spring, so more work is done in stretching it the same distance as a weaker spring. More force is required to stretch the strong spring, so more work is done in stretching it the same distance as a weaker spring.

117.Which requires more fuel: a rocket going from Earth to the Moon or a rocket returning from the Moon to Earth? Why?

More fuel is required for a rocket that leaves the Earth to go to the Moon than the other way around. This is because a rocket must move against the greater gravitational field of the Earth most of the way. (If launched from the Moon to the Earth, then it would be traveling with the Earth's field most of the way.)

118.The energy we need to live comes from chemically stored potential energy in food, which is transformed into other energy forms during the metabolism process. What happens to a person whose combined work and heat output is less than the energy consumed? What happens when the person's combined work and heat output is greater than the energy consumed? Can an undernourished person perform extra work without extra food? Discuss and defend your answers.

More: gain weight or muscle less: Body eats up stored energy Can't do wrok without enrgy so cant do more work without more energy

40.Find the strength of the net force produced by a 30

N force and a 20-N force in each of the following cases: Both forces act in the same direction. The two forces act in opposite directions.- A. 50 N B. 10 N

42.Madison pushes with a 160

N horizontal force on a 20-kg crate of coffee resting on a warehouse floor. The force of friction on the crate is 80 N. Show that the acceleration is 4.0 m/s2.-4m/s/s=80N/20kg

43.Sophia pushes with a 40

N horizontal force on a 4.0-kg box resting on a lab bench. The box slides against a horizontal friction force of 24 N. Show that the box accelerates at 4.0 m/s2.- a=Fnet/m=40 N−24 N/4.0 kg=16 N/4.0 kg=4.0 m/s2

115.When Marie exerts a horizontal force of 200 N to slide a table across a floor at constant velocity, how much friction does the floor exert on the table? Is the force of friction equal and oppositely directed to her 200

N push? Does the force of friction make up the reaction force to her push? Why or why not?- The friction on the table is 200 N, which cancels her 200-N push on the table to yield the zero net force that accounts for the constant velocity (zero acceleration). Although the friction force is equal and oppositely directed to the applied force, the two do not make an action-reaction pair of forces. That's because both forces do act on the same object—the table. The reaction to Marie's push on the table is the table's push back on her. The reaction to the frictional force of the floor on the table is the opposite friction force of the table on the floor.

82.Two 100

N weights are attached to a spring scale as shown. Does the scale read 0 N, 100 N, or 200 N, or some other reading? (Hint: Would the reading differ if one of the ropes were tied to the wall instead of to the hanging 100-N weight?)-

Suggest a bee and a bus make moving at a constant velocity collide, descrube what happens in terms of all of Newton's laws.

NEtwons 1st law states that an object will stay in it's state of motion unless acted on by an outside oforce. This means that the truck will keep going because it's inertia is greater so it will resist the change in motion. It will still have a change, just not as signifcant. Newtons second law staes that a/fnet/m. This means that the truck will have a lesser rate of change than the bee because accleration is inverely proportional to mass. tHis causes the truck to acclerate less and the bee to acelrate more. NEwton's 3rd la wstates that fpor every action there is an equal and oposite reaction. IN this case, the bus and the bee are exerting the same amount of force o n ecah other but the bu's inertia resists the bee's fporce more so it doesn't lokm like they are exerting the same amount of force on each other.

88.Gracie says acceleration is how fast you go. Alex says acceleration is how fast you get fast. They look to you for confirmation. Who's correct?

Neither are because acceleration is the rate at which velocity changes. Gracie was talking about speed, which is a factor of acceleration, but not what acceleration is. Alex said acceleration was how fast something gets fast, or how the rate of change of speed. Speed is not the same as velocity. Velocity is both speed and direction while speed is the distance per unit time. ALex described a component of acceleration but not the whole thing. Alex was closer though and if just said how fast an object's velocity changes, then he would be correct.

114.A farmer urges his horse to pull a wagon. The horse refuses, saying that to try would be futile, for it would flout Newton's third law. The horse concludes that it can't exert a greater force on the wagon than the wagon exerts on itself, so it wouldn't be able to accelerate the wagon. What explanation can you offer to convince the horse to pull?

Net force never comes out of a single ineraction ratehr it comes out of multiple ineractions acting together. Net force cpomes from forces applied to the ground in this instance. It is true though that you can only pull as hard on a horse as hard as the horse can pull back, but net force doesn't coem from that single interaction

What law explained what Galileo couldn't.

Newton's 2nd law of motion

99.Before the time of Galileo and Newton, many learned scholars thought that a stone dropped from the top of a tall mast on a moving ship would fall vertically and hit the deck behind the mast by a distance equal to how far the ship had moved forward during the time the stone was falling. In light of your understanding of Newton's laws, what do you and your classmates think about this idea?

Newton's first law again—when the stone is released it is already moving as fast as the ship, and this horizontal motion continues as the stone falls.

Every object continues in a state of rest, or in a state of motion in a straight line at constant speed, unless acted upon by a net force.

Newton's first law of motion

particles and spherical bodies, as well as to nonspherical bodies sufficiently far apart. .

Newton's law of gravity as written applies to

The acceleration produced by a net force on an object is directly proportional to the net force, is in the same direction as the net force, and is inversely proportional to the mass of the object.

Newton's second law of motion

Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object.

Newton's third law of motion

80.The strong man will push apart the two initially stationary freight cars of equal mass before he alone drops straight to the ground. Is it possible for him to give either of the cars a greater speed than the other? Why or why not?

No because he is in the air and balancing from both of the cars. If he were to try to exert force on one of the cars, he would lose balance and cause himself to exert the same force on the other. It is like Newton's 3rd law of motion, which states that for every action, there is an equal and opposite reaction. He will do one action onto one, but will also do an equal and opposite action on the other one. He will push on one, which will cause him to push on the other one becaus eit is pushing back on him. He is a physical manifestation of NEwton's 3rd law

30.Can we correctly say that hydrogen is a relatively new source of energy? Why or why not?

No because it has been used in the old times to power machines by pushing on a wheel that dips a bit into the water like a gear.

only a change in direction occurs

No component of force is acting in the direction of satellite motion to change its speed only a

83.When you rub your hands together, can you push harder on one hand than on the other?

No, for each hand pushes equally on the other in accord with Newton's third law—you cannot push harder on one hand than the other.

119.Can a dog wag its tail without the tail in turn "wagging the dog"? (Consider a dog with a relatively massive tail.)

No, for in action-reaction fashion, the tail also wags the dog. How much depends on the relative masses of the dog and its tail, and friction between the ground and its feet.

81.Bronco dives from a hovering helicopter and finds his momentum increasing. Does this violate the conservation of momentum? Explain.

No. If we consider Bronco to be the system, then a net force, Earth's pull on him, acts and his momentum changes. So in the system of Bronco only, momentum is not conserved. If, however we consider the system (Bronco + Earth), then all the forces that act are internal forces and momentum is conserved. Both move toward each other with equal and opposite momenta. Momentum is conserved only in systems that are not subject to external forces.

96.Discuss whether or not a stick of dynamite contains force. Similarly, does a fist contain force? A hammer? Defend your answers.

None of these contain force becasue nothinhg can contain a force. They contain a lot of potential energy though, but no force. This is because of NEwton's 1st law. OUtside forces have to act on something to give it force.

53.A firefighter of mass 80 kg slides down a vertical pole with an acceleration of 4 m/s2. Show that the friction force that acts on the firefighter is 480 N.

Note that the weight of the 80-kg firefighter is mg = 80 kg × 10 m/s2 = 800 N. So Fnet = (800 N − f ) = ma = (80 kg)(4 m/s2) = 320 N. So f = 800 N − 320 N = 480 N.

Scientific Method steps

Observe. Closely observe the physical world around you. Recognize a question or a puzzle—such as an unexplained observation. Question. Make an educated guess—a hypothesis—to answer the question. Predict. Predict consequences that can be observed if the hypothesis is correct. The consequences should be absent if the hypothesis is not correct. Test predictions. Do experiments to see whether the consequences you predicted are present. Draw a conclusion. Formulate the simplest general rule that organizes the hypothesis, predicted effects, and experimental findings.

Two assertions of Aristotle held sway for some 2000 years.

One was that heavy objects necessarily fall faster than lighter objects. The other was that moving objects must necessarily have forces exerted on them to keep them moving.

4%.

Ordinary matter, the stuff of stars, cabbages, and kings, makes up only about

So, overall, does ball A or ball B have the greater average speed? (Do you wish to change your answer to Exercise 107?)

Overall, the two will both exit at the same time because A will roll down a straight path with one boost. B will be rolling down with two boosts, but it will then reach an upward hill that will cancel out one of the boosts, so it will slow down long enough for the other one to catch up.

97.In an orbiting space craft, you are handed two identical closed boxes, one filled with sand and the other filled with feathers. Discuss at least a couple of ways that you can tell which is which without opening the boxes.

Poke, kick, or shake the boxes. The one that more greatly resists a change in motion is the one with the greater mass—the one filled with sand.

Scientific method

Principles and procedures for the systematic pursuit of knowledge involving the recognition and formulation of a problem, the collection of data through observation and experiment, and the formulation and testing of hypotheses.

antigravity dark energy

Recent evidence suggests that the universe is expanding and accelerating outward, pushed by an

87.The examples of Exercises 84, 85, and 86 can be explained in terms of momentum conservation. Now explain them in terms of Newton's third law.

Regarding Exercise 84, you exert a force on the boat, (action), and the boat exerts a force on you, (reaction). If your jump lacks sufficient force, you end up in the water. Regarding Exercise 85, if you don't exert a net force on the ball, the ball won't exert a net force on you. So no net force, no change in motion. Regarding Exercise 86, if one throws clothing, the force that accelerates the clothes will be paired with an equal and opposite force on the thrower. This force can provide recoil toward shore.

128.Discuss the advisability of simply removing the sail in the situation discussed in Questions 126 and 127.

Removing the sail will make there be little motion and the motion will be going backwards. This is because when the fan pushes on the sail, it causes the sail to move forward to bounce the air back. It will still be moving because the fan is exerting force on the air and the fan exerts a big force in little distance, so the air exerts little force in a big distance. This is because of the law of conservation of momentum which states that the momentum of a system that does not have an outside force acting on it remains unchanged. This means that the net momentum must equal 0 to be a system. In this case, the fan exerts a big force in little distance, so the air exerts little force in a big distance.

formula for speed

S=D/T

114.Shruti Kumar projects a ball at an angle of 30° above the horizontal. Which component of initial velocity is larger: the vertical or the horizontal? Which of these components undergoes the least change while the ball is airborne? Defend your answer.

STOP RIGHT THERE CRIMINAL SCUM! NOBODY USES AN UNCONFIRMED QUESTION ON MY WATCH

that if d gets bigger by a factor of 3, F gets smaller by a factor of 9.

Saying that F is inversely proportional to the square of d means, for example

what makes science and technology different

Science is concerned with gathering knowledge and organizing it. Technology lets humans use that knowledge for practical purposes, and it provides the instruments scientists need to conduct their investigations.

Force

Simply stated, a push or a pull.

83.Chuck Stone releases a ball near the top of a track and measures the ball's speed as it rolls horizontally off the end of the table. Students make measurements to predict where a can must be placed to catch the ball. How will the ball's speed affect the time it takes to reach the can once the ball leaves the end of the table? (Does a faster ball take a longer time to hit the floor?) Defend your answer.

Since the ball moves horizontally off the edge of the table, speed does not affect the time to reach the can. Time of fall is independent of horizontal velocity.

is the force it exerts against a supporting floor or a weighing scale.

So a broader definition of the weight of something

130.Discuss whether something can have energy without having momentum. Discuss whether something can have momentum without having energy.

Something can have energy without having momentum because the law of conservation of energy states that energy cannot be created nor destroyed, it can only be changed and transferred. When there is no momentum present, the object still has energy in it, potential energy. This is because momentum is inertia in motion which means that an obejct wiuth momentum has kinetic energy in it. Meanwhile, potential energy is energy when something is stationary because of position. This also means that momentum can't exist without energy because it's energy in motion and anything that moves has kinetic energy.

The speed at which the acceleration of a falling object terminates when air resistance balances its weight.

Terminal speed

80.Place a heavy book on a table, and the table pushes up on the book. A friend reasons that the table can't push upward on the book because if it did, the book would rise above the table. What do you say to your friend? Why does this upward push not cause the book to rise from the table?

That is incorrect because the support force opposes with the same amount of force that the weight has. When you push the book down on the table, the table retaliates with the same amount of force as the weight of the book. If it didn't retaliate with force at all, the downward force of the book would cause the book to break through the table, through the ground, and to the center of the Earth. The support force stops when the table doesn't need support to stop the book form going through it or the table is not experiencing any more force pressed upon it.

94.Asteroids have been moving through space for billions of years. A friend says that initial forces applied long ago keep them moving. Do you and your friend agree?

That is true because all objects on earth would keep moving forever because of Inertia but are stopped by natural outside forces like friction, support force, etc. In space, however, there is no natural outside force to stop an object from moving so it will stay moving forever unless an outside force stops it. The object would've been completely still, but someone or something got it moving.

101.On a playground slide, a child has potential energy that decreases by 1000 J while her kinetic energy increases by 900 J. What other form of energy is involved, and how much?

The 100 J of potential energy that doesn't go into increasing her kinetic energy goes into thermal energy—heating her bottom and the slide.

76.A friend says that Alé cannot push on the tree unless the tree pushes back on her, and another friend says that if Alé pushes quickly, the tree won't push as hard on her. Which friend do you agree with, and why?

The 1st friend is correct because Newton's 3rd law states that every action has an equal and opposite reaction, so if the action is that you push on the tree, the reaction is that the tree pushes back on you with an equal amount of force, hence why you don't go backwards from the tree pushing you and why you feel a pushing force when you push on the tree. Also why you won't push through the tree when you push on it.

As mentioned in the Prologue, the 16th-century Polish astronomer Copernicus caused great controversy when he published a book proposing that

The Earth reveolves around the sun

99.At what point in its motion is the KE of a pendulum bob at a maximum? At what point is its PE at a maximum? When its KE is at half its maximum value, how much PE does it possess?

The KE of a pendulum bob is maximum where it moves fastest, at the lowest point; PE is maximum at the highest points. When the pendulum bob swings by the point that marks half its maximum height, it has half its maximum KE, and its PE is halfway between its minimum and maximum values. If we define PE = 0 at the bottom of the swing, the place where KE is half its maximum value is also the place where PE is half its maximum value, and KE = PE at this point. (Via energy conservation: Total energy = KE + PE.)

123.A satellite can orbit at 5 km above the Moon's surface, but not at 5 km above Earth's surface. Why?

The Moon has no atmosphere (because escape velocity at the Moon's surface is less than the speeds of any atmospheric gases). A satellite 5 km above the Earth's surface is still in considerable atmosphere, as well as in range of some mountain peaks. Atmospheric resistance is the factor that most determines orbiting altitude.

The greater the mass of an object, the stronger is the gravitational pull between it and Earth. The double brick in Figure 2.9 for example, has twice the gravitational attraction of the single brick. Why, then, doesn't the double brick fall twice as fast (as Aristotle supposed it would)?

The answer is evident in Newton's second law: the acceleration of an object depends not only on the force (weight, in this case), but on the object's resistance to motion—its inertia. Whereas a force produces an acceleration, inertia is a resistance to acceleration. So twice the force exerted on twice the inertia produces the same acceleration as half the force exerted on half the inertia.

100.Someone standing at the edge of a cliff (as in Figure 1.24) throws a ball straight up at a certain speed and another ball straight down at the same initial speed. If air resistance is negligible, which ball will hit the ground below at greater speed? Or will they both hit at the same speed?

The ball going straight down would because the other one that is thrown up in the air will take longer, but they will have the same speed when they hit the ground. The one thrown up in the air begins to lose all the force used to put it up there. It then begins to gain it all back through acceleration on the way down because gravity is now acting on it in it's direction. The other ball that was thrown straight down will head at the ground at the speed.

120.If you simultaneously drop a pair of tennis balls from the top of a building, they strike the ground at the same time. If one of the tennis balls is filled with lead pellets, will it fall faster and hit the ground first? Which of the two will encounter more air resistance? Defend your answers.

The ball with lead pellets ill hit the ground first because it has a lower surface area/weight ratio and terminal velocity is inversely proportional to the siurface area/weight ratio, this means the ball with pellets will reach it's maximum speed quicker than the ball without lea dpelets in it. It will also have mroe air resistance because air resistanc eis directly proportional to speed and surface area

In Figure 2.15, we see a boxer's fist hitting a massive punching bag. The fist hits the bag (and dents it) while the bag hits back on the fist (and stops its motion). This force pair is fairly large. But what if the boxer were hitting a piece of tissue paper?

The boxer's fist can exert only as much force on the tissue paper as the tissue paper can exert on the boxer's fist. The fist can't exert any force at all unless what is being hit exerts the same amount of reaction force

Descibe the events that take place when you fire a cannon

The cannon and the canon ball exert the sanme amount of force one ecahg other whe the cannon fires because of Newton's 3rd law, but thecannonball accelerates way than the other because of Newton's 2nd law that acceleration is inversely proportional to mass. MEanwhile, Newtons 2nd law also applies to the cannon noyt moving that much becaus eof it's high inertia. The way inertia works applies to Newton's 1st law.

the closer the ellipse is to a circle

The closer the foci are to each other,

Net Force

The combination of all forces that act on an object.

131.Arrange the following four energy transforming devices or processes in the correct order for converting solar energy to the kinetic energy of vehicles: (1) fuel cell, (2) electrolysis, (3) electric motor, (4) photovoltaic cell.

The correct order is (4) photovoltaic cells (convert solar to electric energy), (2) electrolysis (convert electric energy to potential energy of separated hydrogen and oxygen), (1) fuel cells (recombine hydrogen and oxygen to create water and electric energy), (3) electric motor (convert electric energy to kinetic energy).

Parabola

The curved path followed by a projectile under the influence of constant gravity only.

horizantal and vertical motion

The curved path of a projectile is a combination of

the distance between the centers of masses of the objects

The distance term d in Newton's equation is

78.If you throw a raw egg against a wall, you'll break it; but if you throw it with the same speed into a sagging sheet, the egg won't break. Explain, using concepts from this chapter.

The egg thrown against the wall will break because of the shorter impulse time, while the egg thrown against a sagging sheet will not break because of a longer impulse time. An impulse is momentum over a specific period of time. This would mean that if the impulse time is small, the force will be larger because you are gaining/losing momentum in such a quick succession. If the impulse time is bigger, the force would be smaller because it is exerting little force in such a huge time. In terms of the problem, when hitting the wall, it will cause less impulse time, so the force will be greater and break the egg, but when hitting the sheet, it will cause more impulse time, so the force will be smaller.

Potential energy

The energy that matter possesses due to its position:

96.A friend says that when twice as much work is done on a wagon, it will gain twice as much kinetic energy. Another friend say it will gain four times as much kinetic energy. Which friend do you agree with?

The first friend is right because the work energy theorem states that all work done equals the change in kinetic energy. This means that when the double work is exerted on the wagon it will gain double kinetic energy

Copernicus's concept of a Sun-centered solar system was the result of years of studying the motion of the planets. He had kept his theory from the public—for two reasons.

The first reason was that he feared persecution; a theory so completely different from common opinion would surely be taken as an attack on established order. The second reason was reservations about it himself; he could not reconcile the idea of a moving Earth with the prevailing ideas of motion. The concept of inertia was unknown to him and others of his time.

78.When you stand on a floor, does the floor exert an upward force against your feet? How much force does it exert? Why does this force not move you upward?

The floor does exert an upward force on you as you stand on it because Newton's 3rd law states that for every action, there is an equal and opposite reaction. When you stand on the floor the floor exerts a n opposite reaction of force to you standing in it. It exerts an equal amount of force on you as much as you exert on the floor because once again Newton's 3rd law states that for every action there is an equal and opposite reaction. Finally, the reason you are not moving upward is because it will always exert an equal and opposite reaction, so you will be put in equilibrium, mechanical equilibrium to be exact. WHen you are in mechanical equilibrium, you are stationary because the two forces acting on you are more than 0N and the net force of them is equal to 0N.

119.A new member of your discussion group says that, because Earth's gravity is so much stronger than the Moon's gravity, rocks on the Moon could be dropped to Earth. What is wrong with this assumption?

The force of Moon gravity on the rock compared to Earth gravity on the same rock depends on relative distances. The small distance between rocks on the Moon and the Moon compared with the very much larger distance between rocks on distant Earth, finds Moon significantly outpulling Earth. (How much so makes a nice problem: calculate and see.)

air resistance

The force of friction acting on an object due to its motion in air.

its direction of motion, no component of force to pull it forward or backward, and the ball rolls at constant speed.

The force of gravity on the bowling ball is at 90° to____________, so it has _________________

Support Force

The force that supports an object against gravity, often called the normal force.

Weight

The force upon an object due to gravity. More specifically, the force with which a body presses against a supporting surface.

66.As you leap upward from the ground, how does the force that you exert on the ground compare with your weight?

The force you exert on the ground is the exact same as your weight which means the force exerted on you is the exact sae as the force you exert on the ground because Newton's 3rd law states that every action has an equal and opposite reaction. So if you were to exert 10 N on the Earth with a jump, the Earth would exert 10 N of gravitational force on you. I mentioned gravity because weight is the amount of gravity exerted on an object. So you are exerting force on the earth and the earth is exerting force back on you.

109.An apple falls because of its gravitational attraction to Earth. How does the gravitational attraction of Earth to the apple compare? (Does force change when you interchange m1 and m2 in the equation for gravity—m2m1 instead of m1m2?)

The forces between the apple and Earth are the same in magnitude. Force is the same either way, but the corresponding accelerations of each are different.

85.Consider the two forces acting on the person who stands still—namely, the downward pull of gravity and the upward support of the floor. Are these forces equal and opposite? Do they form an action-reaction pair? Why or why not?

The forces must be equal and opposite because they are the only forces acting on the person, who obviously is not accelerating. Note that the pair of forces do not comprise an action-reaction pair, however, for they act on the same body. The downward force, the man's weight, Earth pulls down on man, has the reaction man pulls up on Earth, not the floor pushing up on him. And the upward force of the floor on the man has the reaction of man against the floor, not the interaction between the man and Earth. (If you find this confusing, you may take solace in the fact that Newton himself had trouble applying his 3rd law to certain situations. Apply the rule, A on B reacts to B on A, as in Figure 2.19.)

the weaker the force of attraction, in inverse proportion to the square of the distance between their centers of mass.

The greater the distance of separation d,

127.This situation should elicit good discussion: In an accidental explosion, a satellite breaks in half while in circular orbit about Earth. One half is brought momentarily to rest. What is the fate of the half brought to rest? What happens to the other half? (Hint: Think momentum conservation.)

The half brought to rest will fall vertically to Earth. The other half, in accord with the conservation of linear momentum will have twice the initial velocity, overshoot the circular orbit, and enter an elliptical orbit whose apogee (highest point) is farther from the Earth's center.-128. Yes I do agree. If the horizontal net force is on the left pushing against the already moving force on the right, the velocity pushing on the right must decelerate or accelerate to the left to change the direction. This will happen because the forces pushing left are bigger than the forces pushing right. So if the vehicle's velocity was 10m/s and the acceleration is -5m/s/s, then it would go 10m/s, 5m/s, 0m/s (still). It could go in reverse, but in this case, only the brakes are applied so there is no need to go into the negatives.

68.For each of the following interactions, identify the action and reaction forces. (a) A hammer strikes a nail. (b) Earth gravity pulls down on a book. (c) A helicopter blade pushes air downward.

The hammer exerts force on the nail, which causes the nail to go downwards into whatever it is above. The reaction is that the nail exerts an equal force back on the hammer, hence why you feel an upward force when you hit the nail. Earth's gravity pulls down on the book which gives the book weight and causes it to push down. The reaction is that the book will exert an equal support force (the force that acts to oppose gravity.) on itself, which causes the book to remain stationary and not go through everything downwards.

89.The hang time of a basketball player who jumps a vertical distance of 2 feet (0.6 m) is about 0.6 s. What is the hang time if the player reaches the same height while jumping 4 ft (1.2 m) horizontally?

The hang time will be the same, in accord with the answer to the preceding exercise. Hang time is related to the vertical height attained in a jump, not on horizontal distance moved across a level floor.

63.Which of Aristotle's ideas did Galileo discredit with his inclined plane experiments?

The idea that all objects must have a force keeping them moving for them to keep moving. The incline plane experiments discredited the idea that a continuing force was needed for motion to continue.

99.In tearing a paper towel or plastic bag from a roll, discuss why a sharp jerk is more effective than a slow pull.

The inertia of a whole roll resists the large acceleration of a sharp jerk and only a single piece tears. If a towel is pulled slowly, a small acceleration is demanded of the roll and it unwinds.

Inverse square law

The intensity of an effect from a localized source spreads uniformly throughout the surrounding space and weakens with the inverse square of the distance

113.Some people dismiss the validity of scientific theories by saying they are "only" theories. The law of universal gravitation is a theory. Does this mean that scientists still doubt its validity? Explain.

The misunderstanding here is not distinguishing between a theory and a hypothesis or conjecture. A theory, such as the theory of universal gravitation, is a synthesis of a large body of information that encompasses well-tested and verified hypothesis about nature. Any doubts about the theory have to do with its applications to yet untested situations, not with the theory itself. One of the features of scientific theories is that they undergo refinement with new knowledge. (Einstein's general theory of relativity has taught us that in fact there are limits to the validity of Newton's theory of universal gravitation.)

60.The Moon travels in a nearly circular path around Earth. If somehow gravitation between Earth and Moon disappeared, how would the Moon's path differ?

The moon would gon away from the earth in a constant speed at a syraight line forever unless acted on by an outside force. This is because of NEwton's 1st law. Itb would be moving because it moves around the earth in a circle so it would be like a rockj in a a sling

63.Why is a massive cleaver more effective for chopping vegetables than a lighter knife of the same sharpness?

The more massive cleaver tends to keep moving when it encounters the resisting force of the vegetables, cutting them more effectively.

74.If the vine that supports the monkey breaks, what is then the net force on the monkey?

The net force is whatever the downard force is because the support force has been overpowered and is

work energy theorem

The net work done on an object equals the change in kinetic energy of the object.

81.Elements beyond the naturally occurring elements that have been discovered that are named Neptunium and Plutonium. How was the naming process related to discovery of new planets?

The new elements were so named in honor of the prior discoveries of Neptune and Pluto.

Ellipse

The oval path followed by a satellite. The sum of the distances from any point on the path to two points called foci is a constant. When the foci are together at one point, the ellipse is a circle. As the foci get farther apart, the ellipse becomes more eccentric.

Efficiency

The percentage of the work put into a machine that is converted into useful work output.

90.In a movie, the hero jumps straight down from a bridge onto a small boat that continues to move with no change in velocity. What physics is being violated here?

The person has mass and so does the boat, so when he lands on the boat the boat gains mass, but the momentum must remainthe same, so in order to do that the speed has to go down, which this doesn't provide

92.If your friend pushes a stroller four times as far as you do while exerting only half the force, which one of you does more work? How much more?

The person who pushed the stroller four times as far because work is force x distance. This means that if you pushed with 2 N for 4 m and he pushed with 1 N for 16 m, he would technically have done more work because you would have only doen 8 joules of work and he would have done 16 joules of work. This shows he is doing twice as much work as you are. If it were force and time we would be talking about momentum and whoever did 4 times as much time would have less momentum than the person who didn't do that.

139.Consider a bob attached by a string—a simple pendulum—that swings to and fro. (a) Why does the tension force in the string not do work on the pendulum? (b) Explain, however, why the force due to gravity on the pendulum at nearly every point does do work on the pendulum. (c) Where is the single position of the pendulum where "no work by gravity" occurs?

The physics here is similar to that of the ball on the alley in the previous problem. Tension in the string is everywhere perpendicular to the arc of the pendulum, with no component of tension force parallel to its motion.In the case of gravity, a component of gravitational force on the pendulum does exist parallel to the arc, which does work and changes the KE of the pendulum.When the pendulum is at its lowest point, however, there is no component of gravitational force parallel to motion. At that instant of motion, gravity does no work (as it doesn't when the pendulum hangs at rest when the string is vertical).

Impulse

The product of the force acting on an object and the time during which that force acts on that object.

Work

The product of the force and the distance moved by the force:

Inertia

The property by which objects resist changes in motion.

Energy

The property of a system that enables it to do work.

Mass

The quantity of matter in an object. More specifically, a measure of the inertia (or sluggishness) that an object exhibits in response to any effort made to start it, stop it, deflect it, or change in any way its state of motion.

volume

The quantity of space an object occupies.

Acceleration

The rate at which velocity changes with time; the change in velocity may be in magnitude or direction or both, and it is usually measured in units of m/s2.

Power

The rate of doing work:

107.Newton tells us that gravitational force acts on all bodies in proportion to their masses. Why, then, doesn't a heavy body fall faster than a light body?

The reason that a heavy body doesn't fall faster than a light body is because the greater gravitational force on the heavier body (its weight), acts on a correspondingly greater mass (inertia). The ratio of gravitational force to mass is the same for every body—hence all bodies in free fall accelerate equally. And it's true not just near the Earth, but anywhere. (This is illustrated back in Figure 2.10.)

Friction

The resistive force that opposes the motion or attempted motion of an object past another object with which it is in contact, or through a fluid.

21.Compared with the work that the brakes must supply to stop a car moving at some original speed, how much more work must the brakes supply to stop that car if it is moving four times as fast as the original speed? How do the respective stopping distances compare?

The same amount of work used to get to teh original speed. The stopping speeds differ from the car speeding up slowly and the brakes almost instantly stopping it.

Newton

The scientific unit of force.

104.On which of these hills does the ball roll down with increasing speed and decreasing acceleration along the path? (Use this example if you wish to explain to someone the difference between speed and acceleration.)

The second one because it will be accelrating quickly at the beiginning and gaining speed, but when it arrives at the middle and the ground becomes less steep, it will slowly decrease accelration but accleration will still be happening on the ball because if it acc was 10m/s/s, the ball would increase 10m/s, when it decelerates to 9m/s/s the ball will be 19m/s it is not stopping but is decelerating.

105.You're on a rooftop and you throw one snowball downward to the ground below and another upward. The second snowball, after rising, falls and also strikes the ground below. If air resistance can be neglected, and if downward and upward initial speeds are the same, how do the speeds of the snowballs upon striking the ground compare? (Use energy conservation to arrive at your answer.)

The snowballs strike the ground with the same speed, whether thrown upward or downward. The snowballs start with the same energy at the same place, so they will have the same energy when they reach the ground. This means they will strike with the same speed assuming negligible air resistance. If air resistance is a factor, then the snowball thrown upward will dissipate more energy in its longer path and strike with somewhat less speed. But with negligible air resistance, both hit the ground at the same speed (but at different times).

gravitational field.

The space surrounding all objects with mass is energized with a

velocity

The speed of an object and specification of its direction of motion.

Escape speed

The speed that a projectile, space probe, or similar object must reach to escape the gravitational influence of Earth or of another celestial body to which it is attracted.

67."It's not the fall that hurts you; it's the sudden stop." Translate this common saying into Newton's laws of motion.

The sudden stop involves a large acceleration. So in accord with a=Fm, a large a means a large F. Ouch!

79.An empty jug of weight W is at rest on a table. What is the support force exerted on the jug by the table? What is the support force when water of weight w is poured into the jug?

The support force on the jug is W. When water w is added, the support force is W + w.

101.Consider a ball at rest in the middle of a toy wagon. When the wagon is pulled forward, the ball rolls against the back of the wagon. A friend asks what force pushes the ball to the back of the wagon. Interpret this observation in terms of Newton's first law.

The tendency of the ball is to remain at rest. From a point of view outside the wagon, the ball stays in place as the back of the wagon moves toward it. (Because of friction, the ball may roll along the wagon surface—without friction the surface would slide beneath the ball.)

hang time

The time that one's feet are off the ground during a vertical jump.

72.A monkey hangs stationary at the end of a vertical vine. What two forces act on the monkey? Which force, if either, is greater?

The two forces acting on the monkey are gravity and support force. The monkey is in equilibrium, which means neither force is greater because if the support force were higher, the monkey would be floating upwards, and if the downward force were higher, the vine would break. The monkey is in mechanical equilibirum because there are still forces acting on him, but he is not moving.

77.What two forces act on you while you are in a moving elevator? When are these forces of equal magnitude and when are they not?

The two forces are the normal force and mg, which are equal when the elevator doesn't accelerate, and unequal when the elevator accelerates.

kilogram

The unit of mass. One kilogram (kg) is the mass of 1 liter (L) of water at 4°C.

97.For the pulley system shown, what is the upper limit of the weight the strong man can lift?

The upper limit the man can lift is his own weight, for beyond that his feet leave the ground.

Equilibrium rule

The vector sum of forces acting on an object that is not accelerating equals zero

the greater the distance covered in each successive second, the vertical distances of travel decrease with time on the way up.

The vertical component is exactly the same as for an object falling freely straight down, as shown at the left in Figure 4.12. The faster the object falls,______________________. Or, if the object is projected upward,________________

51.If you stand next to a wall on a frictionless skateboard and push the wall with a force of 40 N, how hard does the wall push on you? Show that if your mass is 80 kg, your acceleration is 0.5 m/s2 away from the wall.

The wall pushes on you with 40 N. a=Fnet/m=40 N/80 kg=0.5 m/s2.

Conservation of energy for machines

The work output of any machine cannot exceed the work input. In an ideal machine, where no energy is transformed into thermal energy,

135.Your friend says that one way to improve air quality in a city is to synchronize traffic lights so that motorists can travel long distances at constant speed. Discuss the physics that supports this claim.

The work-energy theorem applies here. Your friend is correct, for changing KE requires work, which means more fuel consumption and decreased air quality.

82.A pair of skaters who are initially at rest push against each other so that they move in opposite directions. What is the total momentum of the two skaters as they move apart? Is there a different answer if their masses are not the same?

Their momentum is the same. This is true because momentum before the collision equals the momentum after the collision. In this case, the two balls' momentum used to hit each other before the collision is going to be as much as the momentum used as they move apart. Their momentum will also not change if their masses are different. Their momentums will not be different because the higher the mass, the less distance, so one of the skaters will have a higher mass and a shorter distance than the other depending on who has the higher mass. This is true because momentum=force x mass.

84.One ultralight aircraft travels due north at 100 km/h while another travels due south at 100 km/h. Are their speeds the same? Are their velocities the same? Explain.

Their speeds are the same, but their velocity is not. Speed is only the distance per unit time, while velocity is speed and direction. They may have the same speed, but one is moving south and the other is moving north. Velocity has to have both the direction and the speed for it to be velocity. If it has the same speed but different directions, the velocity is different. If it has the same direction but different speeds, the velocities are different as well. This means the speed is the same, but the velocity is different.

93.A racing car travels along a straight raceway at a constant velocity of 200 km/h. What horizontal forces act, and what is the net force acting on the car?

There are two horizontal forces on the car: road friction acting on the tires, and air resistance in the opposite direction. At constant velocity there is no acceleration. The net force is therefore zero—meaning the force on the tires is equal and opposite to the force of air resistance.

113.Consider Andrea's swinging balls apparatus. If two balls are lifted and released, momentum is conserved because at impact, two balls pop out the other side with the same speed as the released balls. But momentum would also be conserved if one ball popped out at twice the speed. Explain why this never happens.

There is more to the "swinging balls" problem than momentum conservation, which is why the problem wasn't posed in the previous chapter. Momentum is certainly conserved if two balls strike with momentum 2mv and one ball pops out with momentum m(2v). That is, 2mv = m2v. We must also consider KE. Two balls would strike with 2(½mv2) = mv2. The single ball popping out with twice the speed would carry away twice as much energy as was put in: ½m(2v)2= ½m(4v2) = 2mv2. This is clearly a conservation of energy no no!

90.What is the acceleration of a car that moves at a steady velocity of 100 km/h for 100 s? Why is this question an exercise in careful reading as well as in physics?

There is no acceleration because a steady or constant velocity doesn't accelerate.

94.Two people of the same weight climb a flight of stairs. The first person climbs the stairs in 30 s, and the second person climbs them in 40 s. Which person does more work? Which uses more power?

They have the same amount of work done. This is because the formula for work is force x distance. We know that they have the same weight and went up the same pair of stairs (gone the same distance). If we were to throw some numbers in there, both of their weights are 10 N and they went up a 10 m staircase. This would mean they each exerted 100 Joules of force. Power, on the other hand, is a different story. Power is like acceleration for work. It is the rate at which work is done. That would menja that the formula is work/time. If we added our numbers back again: 100 J/ 30s and 100 J/ 40s. We would get 3.33333...J/s/s for the 30s person and 2.5J/s/s for the 40s person.

76.In terms of impulse and momentum, why do airbags in cars reduce the chances of injury in accidents?

They increase the time of impulse. An impulse is momentum over a specific period of time. This would mean that if the impulse time is small, the force will be larger because you are gaining/losing momentum in such a quick succession. If the impulse time is bigger, the force would be smaller because it is exerting little force in such a huge time. In this case, airbags reduce the chance of injury by puffing up in front of you with a cushiony, pillow-like, inflatable item. This causes your time of impulse from the crash itself to you hitting something hard to increase drastically. THis will cause you to exert such a small amount of force in such high time that you would either hit the thing in front of you at a much lower speed or your force would go to 0N and you wouldn't even hit the thing in front of you

two balls roll down hill. one is heavy, one is light. they roll down the hill at the same time. Why?

They roll at the same force/mass ratio

118.Ken and Joanne are astronauts floating some distance apart in space. They are joined by a safety cord whose ends are tied around their waists. If Ken starts pulling on the cord, will he pull Joanne toward him, or will he pull himself toward Joanne? Explain what does happen.

They will both head to the middle of the rope because of newton's 3rd law. If one had more mass than the ptehr they would meet closer to whoever has the more mass (Newton's 1syt law)

102.Consider the identical balls released from rest on tracks A and B, as shown. When they reach the right ends of the tracks, which will have the greater speed? Why is this question easier to answer than the similar one (Discussion Question 107) in Chapter 1?

They will have the same speed because of the law of conservation of energy. The law states that all energy is not created nor destroyed, it is transferred and undergoes change. In this case, the two balls roll down a hill. The second one at the start has more potential energy transferred to it by gravity and other forces than the first one. This means that when it rolls down the hill, it will gain more kinetic energy on the way down. On the way back up on the hill, it will gain potential energy from the hill and since potential henry has no motion involved, it slows down the ball. The other ball just gains kinetic energy and doesn't run into any other variables. This is easier than last time because it doens tinvolve adding or subtracting, it's purely just changing

88.Suppose that one of the people in Exercise 87 has twice the mass of the other. How far does each person slide before they meet?

They will slide more towards the left if the astronuat with twice the mass of the otehr is on the ,eft because the greater mass the greater the inertia and the greater the inertia, then more resistance in changing a form of motion. Newton's 2nd LAw and NEwton's 1st law. Newtons 3rfd Law.

76.When you push downward on a book that is at rest on a table, you feel an upward force. Does this force depend on friction? Defend your answer.

This force does not depend on friction because friction is an opposing force when an object is pushed passed another through contact or through a fluid. The book is pushed against the table over past it. The force that is actually acting on the object is the support force. Support force is the upward force that opposes gravity. You are pushing the book downward like gravity is pushing everything else downward, so the support force is countering that by pushing upwards, which is the force you are feeling when you push the book on the table.

140.Consider a satellite in a circular orbit above Earth's surface. In Chapter 4 we will learn that the force of gravity changes the direction of motion of a satellite (and keeps it in a circle) but does NOT change its speed. Work done on the satellite by the gravitational force is zero. What is your explanation?

This is because of inertia. Inertia is an objects tendency to continue in it's state of motion forever unless acted on by an outside force. In this case, the direction is the only thing changed, so there is no real force being exerted. The only reason it moves is because a force was applied long ago and it just keeps on moving. Now the formula for work is force x distance. There may be a distance, but there is no force acting. This means that it would be like 0 N x 10 m (example distance). That would equal 0. NO ENERGY SO NO WORK

114.Discuss the physics that explains how the girl in Figure 3.29 can jack up a car while applying so little force.

This is because of the law of conservation of energy for machines. The law states that the input force times the input distance equals the output force time the output distance. This means that no matter what the girl exerts as the input, the output will equal her input. She had added 50 N over 25 cm, so in order to equal out her input and still have a weight of 5000 N, it only moves 0.25 cm. This way, the two equal each other out. (little force; big distance) (big force; little distance)

91.Freddy Frog drops vertically from a tree onto a horizontally moving skateboard. The skateboard slows. Give two reasons for the slowing, one in terms of a horizontal friction force between Freddy's feet and the skateboard, and one in terms of momentum conservation.

This is similar to the previous exercise. In terms of force, Freddy's feet are brought up to speed when they make contact with the moving board. The friction force that brings him up to speed is countered by the same amount of force on the board in the opposite direction, slowing the board. In terms of momentum conservation: Since no external forces act in the horizontal direction, the momentum after the board catches Freddy equals the momentum before. Since Freddy's mass is added, velocity must decrease.

134.This may seem like an easy question for a physics buff to answer: With what force does a 10 N rock strike the ground if it is dropped from a rest position 10 m high? In fact, the question cannot be answered unless you have more information. What information is needed to answer this question, and why?

Time of impact (impulse). Soft, more distance, less force. Hard, less distance, more force

Newtons 3rd law simplieifed

To every action there is always an opposed equal reaction.

Formulas for falling objects starting from a rest position

V=G*T

Formula for change in velocity

V=Vf-Vi

The symbol Σ stands for

Vector of the sum

horizantal and vertical componemnts

Velocity is a vector quantity, and a velocity vector at an angle has

104.Suppose that you're in a moving car and the engine stops running. You step on the brakes and slow the car to half speed. If you release your foot from the brakes, will the car spontaneously speed up a bit, or will it continue at half speed and slow due to friction? Defend your answer.

WHen you slow down your inertia jerks you forward from still beng in the preivious motion of being fast and when you release the brales it jerks you back from being in the previous motion of slow. You are not speeding up, you will, however slow down due to friction.

gravitation

We all know that Earth is round. But why is Earth round?

129.Suppose that three astronauts outside a spaceship decide to play catch. All three equally strong astronauts have the same mass. The first astronaut throws the second astronaut toward the third one and the game begins. Describe the motion of the astronauts as the game proceeds. How long will the game last?

We assume the equal strengths of the astronauts means that each throws with the same speed. Since the masses are equal, when the first throws the second, both the first and second move away from each other at equal speeds. Say the thrown astronaut moves to the right with velocity V, and the first recoils with velocity negative V. When the third makes the catch, both she and the second move to the right at velocity V/2 (twice the mass moving at half the speed, like the freight cars in Figure 3.13). When the third makes her throw, she recoils at velocity V (the same speed she imparts to the thrown astronaut) which is added to the V/2 she acquired in the catch. So her velocity is V + V/2 = 3V/2, to the right—too fast to stay in the game. Why? Because the velocity of the second astronaut is V/2 minus V = negative V/2, to the left—too slow to catch up with the first astronaut who is still moving at negative V. The game is over. Both the first and the third got to throw the second astronaut only once! So the game ends with one throw by each.

Describe the ascent from the first floor of an elevator to the 4th floor while you stand on a scale

We start at the bottom and you read your weight. The elevator is motionless. It then begins to shift from the bottom floor to the first you then begin to gain speed and the scale read more than your weight becuse your inertia is resisting the change in motion. From the first floor to the 3rd floor, you will be moving at a constant velocity and you will read your original weight. When you get from the 3rd to the 4th floor, you begin to slow down andthe scale reads less than your orginal weight becasue your inertia is still going up. When you finally reach the 4th floor, the elevatyor will be ata a stop and your weight will read it's original agaon.

39.A Honda Civic hybrid weighs about 2900 pounds. Calculate the weight of the car in newtons and its mass in kilograms. (FYI, 0.22 lb = 1 N; 1 kg on Earth's surface has a weight of 10 N.)

Weight in newtons: 2900lb×1N/0.22 lb=13,182 N. Mass in kg: 13,182 N×1 kg/10 N=1318 kg.

perturbations

When Saturn is near Jupiter, its pull disturbs the otherwise smooth path traced by Jupiter. Both planets "wobble" about their expected orbits. The interplanetary forces causing this wobbling are called

79.In terms of impulse and momentum, when a boxer is being hit, why is it important that he or she move away from the punch? Why is it disadvantageous to move into an oncoming punch?

When a boxer moves away from an incoming punch, the time of contact is extended, which lessens the force. When moving into a punch, the time of contact is decreased, which increases the force (ouch).

72.Free fall is motion in which gravity is the only force acting. (a) Explain why a skydiver who has reached terminal speed is not in free fall. (b) Explain why a satellite circling Earth above the atmosphere is in free fall.

When a skydiver is in terminal speed, his velocity equals air resistance, so he is not getting faster or slower, he is as fast as he can go. He is not in free fall because air resistance is acting on him and pushing upwards enough to add an equal amount of force upwards to the amount of force downwards. The satallite on the other hand

88.In the previous chapter, rocket propulsion was explained in terms of Newton's third law. That is, the force that propels a rocket is from the exhaust gases pushing against the rocket, the reaction to the force that the rocket exerts on the exhaust gases. Now explain rocket propulsion in terms of momentum conservation.

When lifting off the exhaust gas exerts a force on the rocket, which causes it to start to activate it's momentum, and according to the law of conservation of momentum, the momentum of a system that does not have an outside force acting on it remains unchanged. This means the rocket will also exert a force back on the exhaust ags, which will start up it's momentum as well. Neglecting air resistance and gravity, there are no outside forces to interfere with this, so the outside force on it is unchanged. The reason the rocket is moving up, though, is because the rocket has more mass, which means it will resist the momentum in the opposite direction by the exhaust gas more than the exhaust gas can resist the momentum exerted by the rocket. They still have the same momentum, just in different numbers. Gas has barely any mass but huge disatcne and the rocket has barely any distance but huge mass

126.An ice sailcraft is stalled on a frozen lake on a windless day. The skipper sets up a fan as shown on the next page. If all the wind bounces backward from the sail, discuss whether or not the craft will be set in motion. If so, in what direction?

When the air hits the sail it bounces off the boat and causes exerts momenutm on the sail which causes the sail to push the sail forward.

103.Why do you lurch forward in a bus that suddenly slows down? Why do you lurch backward when it picks up speed? What law applies here?

When the bus slows, you tend to keep moving at the previous speed and lurch forward. When the bus picks up speed, you tend to keep moving at the previous (lower) speed and you lurch backward. The law of inertia applies in both cases.

95.When you toss a coin upward, what happens to its velocity while it is ascending? What happens to its acceleration? (Neglect air resistance.) What is its acceleration at the top of its path?

When the coin goes up the velocity decreases by 10 m/s each second. Its acceleration, however, remains constant (which is why the constant change of 10 m/s each second). At the top its acceleration is 10 m/s2.

107.When the mass of a moving object is doubled, with no change in speed, by what factor is its momentum changed? By what factor is its kinetic energy changed?

When the mass is doubled with no change in speed, both momentum and KE are doubled.

84.You are at the front of a floating canoe near a dock. You leap, expecting to land on the dock easily. Instead you land in the water. Explain in terms of momentum conservation.

When you leap from the canoe, according to the law of conservation of momentum, the momentum of a system that does not have an outside force acting on it remains unchanged. You exert a high force and you will go little disatcne while the boat will exert bacl a small force and a big distance. Also, the boat canm't exert as much force back on you because of Newton's 3rd law so you can only exeert as kuch foce on it as it can exert back.

79.Why can you exert greater force on the pedals of a bicycle if you pull up on the handlebars?

When you pull up on the handlebars, the handlebars in turn pull down on you. This downward force is transmitted to the pedals.

113.This is a scenario common to many physics students: You push a heavy car by hand. The car, in turn, pushes back with an opposite but equal force on you. Doesn't this mean that the forces cancel one another, making acceleration impossible? Resolve the misunderstanding underlying this question.

When you push the car, you exert a force on the car. When the car simultaneously pushes back on you, that force is on you—not the car. You don't cancel a force on the car with a force exerted on you. For cancellation, the forces have to be equal and opposite and act on the same object. Two equal and opposite forces would have to act on the car for cancellation.

121.What is the argument that the energy provided by a hydrogen fuel cell is actually solar energy?

Whether hydrogen is extracted from water by electrolysis or by the burning of fossil fuels, the hydrogen initially was bonded via energy from the Sun.

102.If you're in a car at rest that gets hit from behind, you can suffer a serious neck injury called whiplash. Discuss how whiplash involves Newton's first law and why headrests are standard on today's cars.

Whiplashes are like Newton's first law of motion. Newton's 1stb law of motion states that an object will remain in its state of motion unless acted upon by an outside force. This way, when an object suddenly exerts a large amount of force from moving fast like when stepping on the gas in a car or being rear ended, you will suddenly jerk backwards from the high sudden force you just generated with the car. This will cause your neck to build up a huge amount of inertia because of the sudden high force and pull back, now it is like pulling hard a paper towel roll. Only part of your neck will jerk forward so it will hurt badly. Headrests are now in cars so when a car goes fast instead of jerking backwards, you will just exert a force on the headrest and thanks to Newton's 3rd law of motion (all actions have equal and opposite reactions) your head will be stationary and not whip;lash you.

The answer is that gravity pulls straight downward with no component of force acting forward or backward.

Why doesn't the gravity that acts on the bowling ball change its speed?

80.To throw a ball, do you exert an impulse on it? Do you exert an impulse to catch it if it's traveling at the same speed? About how much impulse do you exert, in comparison, if you catch it and immediately throw it back again? (Imagine yourself on a skateboard.)

Yes because as you hold the ball back to throw it and accelerate, the ball begins to build up momentum because you are moving it faster and faster until it leaves your hand. Impulse is the time it takes to get to a certain momentum. You also exert an impulse to catch the ball because you are catching it and slowing it down to a stop over time. Or you are decreasing it's momentum over time. You exert the same amount of impulse on it as you used to catch it because when something bounces it uses the exact same amount of momentum used to hit the ground

94.If it were not for air resistance, would it be dangerous to go outdoors on rainy days? Defend your answer.

Yes because of Newton's 1st and 3rd law of motion. His first law states that any object in motion stays in motion unless acted upon by an outside force. His third law states that every action has an equal and opposite reaction. This means that when the object is falling, air resistance or an outside force builds up to equal out the force of the rain droplets, thus making them have low speed when falling. Without this, the rain would keep increasing more and more and more until it is at a crazy speed when it hits the ground. It would move like a bullet and definitely hurt when it hits you.

10.When a cannonball is fired, momentum is conserved for the system of cannon + cannonball. Would momentum be conserved for the system if momentum were not a vector quantity? Explain.

Yes because the mass can still be unchanged. A vector quantity is a quantity whose description includes magnitude and direction

133.Does a car burn more fuel when its lights are turned on? Does the overall consumption of fuel depend on whether the engine is running while the lights are on? Discuss and defend your answers.

Yes, a car burns more fuel when its lights are on. The overall consumption of fuel does not depend on whether or not the engine is running. Lights and other devices operate via a battery, which can eventually "run down." The energy used to recharge the battery ultimately comes from the fuel. (Hence there's no "free lunch.")

75.We know that Earth pulls on the Moon. Does it follow that the Moon also pulls on Earth?

Yes, both pulls make up an interaction; neither can exist without the other. Earth cannot pull on the Moon unless Moon simultaneously pulls on Earth.

111.If your momentum is zero, is your kinetic energy necessarily zero also?

Yes, if it is solely you, which would mean your speed is zero. But a system of two or more objects can have zero net momentum, yet have substantial KEs.

136.Does the electric power produced by wind powered generators affect the speed of the wind? That is, would locations behind the wind blades be windier if the generators weren't there?

Yes. This is because of the law of conservation of energy. The law states that all energy canot be created nor destroyed. It rather can be transferred or changed. This means that when the linetic energy of the wind passes through the generator, the geberoatir converts the kinetic energy into electric energy and transfers it into the generator while the rest of the remaining kinetic energy passes through.

98.Each of the vertebrae forming your spine is separated from its neighbors by discs of elastic tissue. Each step you take acts on your spine like a small jump. Can you think of a reason why you are a little shorter in the evening than you are in the morning? (Hint: Think about the hammerhead in Figure 2.2.)

You are shorter in the evening because the force of inertia is acting in your vertebrates. Newton's 1st law of motion states that every object will stay in its position of motion until it is acted upon by an outside force. This is because of something called inertia which is an object's tendency to resist changes in motion. So, your vertebrates will begin to start building up inertia becasue of gravity pulling down on you the more steps you take and begin to make the small jumps less by pulling down on them to hold them into place and eventually bring them to a stationary position as they were meant to be. SInce they are pulled back down, your height shortens.

75.To begin your wingsuit flight, you step off the edge of a high cliff. Why are you then momentarily weightless? At that point, is gravity acting on you?

You are weightless because of no support force. The force of gravity is nevertheless acting on you, and will be the only force on you until air resistance builds up.

121.Another new member of your discussion group says the primary reason why astronauts in orbit feel weightless is that they are being pulled by other planets and stars. Why do you agree or disagree?

You disagree, for the force of gravity on orbiting astronauts is almost as strong as at Earth's surface. They feel weightless because of the absence of a support force.

61.To pull a wagon across a lawn at constant velocity, you must exert a steady force. Reconcile this fact with Newton's first law, which states that motion at constant velocity indicates no force.

You exert a force to overcome the force of friction. This makes the net force zero, which is why the wagon moves without acceleration. If you pull harder, then net force will be greater than zero and acceleration will occur.

91.When your car moves along the highway at constant velocity, the net force on it is zero. Why, then, do you continue running your engine?

You run your engine to provide a force large enough to overcome friction. A net force of zero requires you provide this force.

95.Why do you run out of breath when running up the stairs but not when walking up the stairs?

You use more power when doing the same work in a shorter time. Hence the quicker exertion of energy makes you more likely to run out of breath.

62.Your empty hand is not hurt when it bangs lightly against a wall. Why does your hand hurt when it bangs against the wall while carrying a heavy load? Which of Newton's laws is most applicable?

You will have more mass on yourself with the bowling ball in hand which give syou more inertia. Inertiqa is an objects tendancy to resist chanegs in motion. This means when you collide with thye wall, the inertia you have will cause your hand to exert the same amount of force on the fall soon because when you use just your hand, the you have less inertia so the wall stops you form hurting yourself by exerting force. Whe you use a bowling ball the inertia is more so the wall has more truble stopping you so you exeet the force still and possibly hrut your hand by forcing it hard on the wall.

95.In answer to the question "What keeps Earth moving around the Sun?" a friend asserts that inertia keeps it moving. Correct your friend's erroneous assertion.

Your friend should learn that inertia is not some kind of force that keeps things like Earth moving, but is the name given to the property of things to continue as they are doing when no external force acts. So your friend should say that nothing is necessary to keep the Earth moving. Interestingly, the Sun keeps it from following the straight line path it would take if no forces acted, but it doesn't keep it moving. Nothing does. That's the concept of inertia. We distinguish between what makes an object begin moving, and what keeps it moving.

67.If Earth somehow expanded to a larger radius, with no change in mass, how would your weight be affected? How would it be affected if Earth instead shrunk? (Hint: Let the equation for gravitational force guide your thinking.)

Your weight would decrease if the Earth expanded with no change in its mass and would increase if the Earth contracted with no change in its mass. Your mass and the Earth's mass don't change, but the distance between you and the Earth's center does change. Force is proportional to the inverse square of this distance.

how do those 4 things go hand in hand

Zero net force is the definition of equilibriyum, equilibium not accelrationg, zero accelration is moving at a constant veloicty, moving with 0 accelration, but there are still two forces actng on it that cancel each other out, giving you zero accelration.

Objects don't speed up, slow down, or change direction unless

a force acts

We can see from the definition that a moving object can have a large momentum if it has

a large mass, a high speed, or both.

When a hypothesis has been tested over and over again and has not been contradicted, it may become known as

a law or principle

61.Three pucks, A, B, and C, are sliding across ice at the noted speeds. Air and ice friction forces are negligible. (a) Rank, from greatest to least, the force needed to keep the pucks moving. (b) Rank, from greatest to least, the force needed to stop them in the same time interval.

a. A=B=C (no force) b. C, B, A

in x=a/b x is directly proportional to ___ and inversely proportionl to ____

a. B.

formula for terminal velocity

a=Net force/m=mg-R/m

35.In Chapter 1 acceleration is defined as a=ΔvΔt. Show that on an inclined plane, the acceleration of a cart that gains 6.0 m/s each 1.2 s is 5.0 m/s2.

a=Δv/Δt=6.0 m/s/1.2 s=5.0 m/s2

The term supernatural literally means

above nature

Energy, on the other hand, is

abstract. We cannot see, smell, or feel most forms of energy.

40.When two horizontal forces are exerted on the car in Problem 39, 220 N forward and 180 N backward, the car undergoes acceleration. What additional force is needed to produce non

accelerated motion?-40 N backwards

Most moving things undergo variations in their motion. We say they undergo

acceleration

Newtons second law of motion in equation form

acceleration=net force/mass

Scientists must

accept their experimental findings even when they would like them to be different.

We can call one force the _________ and the other the _____________reaction force

action force; reaction force

R stands for

air resistance

Galileo said (in absence of air drag)

all objects regardless of weight fall at the same rate.

74.Why do the passengers in high

altitude jet planes feel the sensation of weight, while passengers in the International Space Station do not?-74. The passengers feel the sensation of weight because they have a support force. Weight is basically how hard you press down on something or in more professional terms the force on an object due to gravity. The passengers feel weight because they are riding a vehicle where when they stand or sit on it, they feel the force of their weight pushed back on them due to support force equaling out the force exerted on it. Meanwhile, the astronauts are in a state of sustained weightlessness. Weightlessness is another way of saying free fall: no support force, under the influence of gravity alone. The astronauts are just floating so they have no support force pushing back up on them to make them feel the force they exert on it.

what led newton to make the law of universal gravitiation

an apple falling from a tree

A scientific hypothesis, on the other hand, is

an educated guess that is only presumed to be factual until supported by experiment.

Why is continues the key word in Newton's first law

an object continues to do whatever it happens to be doing unless a force is exerted upon it. If the object is at rest, it continues in a state of rest.On the other hand, if an object is moving, it continues to move without changing its speed or direction,

the acceleration of free fall is independent of

an objects mass

73% of the universe

antigravity dark energy that makes up some .

When we apply physics, chemistry, and geology to other planets and to the stars,

astronomy

Only when there is no force at all, or when two or more forces combine to zero, can an object

be in equilibrium

The cardinal rule in science is that all hypotheses must

be testible

110.How does the terminal speed of a parachutist before opening a parachute compare to the terminal speed after opening a parachute? Why is there a difference?

before opening the parachute you have a faster terminal velocity because you have a lower surface area/weight ratio. When you deploy your parachute, you have a higher surface area/weight ratio

Constant velocity, on the other hand, means

both constant speed and constant direction.

mpulses are greater when an object

bounces

56.In cases A, B, and C, the crate is in equilibrium (no acceleration). Rank, from greatest to least, the amounts of friction between the crate and the floor in these three cases.

c,b,a

directly proportional to the product of their masses and inversely proportional to the square of the distance separating them.

ccording to Newton, any body attracts any other body with a force that is

biologists speak of the

cell theory.

You cannot change speed without

changing velocity

he Chinese and Polynesians were

charting the stars and planets

28.What is the ultimate source of the energy supplied by fossil fuels, dams, and windmills?

chemical energu

Kinetic energy and potential energy are two of the many forms of energy, and they underlie other forms of energy like

chemical energy, nuclear energy, sound, and light

Underlying biology is __________, and underlying chemistry is ________

chemistry; physics

Galileo measured speed by

comparing the distance covered with the time it takes to move that distance.

To better understand that the table pushes up on the book, compare the case of compressing a spring (Figure 1.13). If you push the spring down, you can feel the spring pushing up on your hand. Similarly, the book lying on the table

compresses atoms in the table, which behave like microscopic springs. The weight of the book squeezes downward on the atoms, and they squeeze upward on the book. In this way, the compressed atoms produce the support force.

The key word in this Newton's first law of motion is

continues

Art is about ___________. Science is about ___________. Religion is about __________.

cosmic beauty; cosmic order; cosmic purpose

When something slows down, we often call this

deceleration

Directly and inversely proportional is like saying

directly/indirectly negligable

Speed is directly proportional to

distance

25.If a machine multiplies force by a factor of 4, what other quantity is diminished, and by how much?

distance by 4

horizontal ranges,

distances traveled horizontally.

16.A car is raised a certain distance in a service station lift and therefore has potential energy relative to the floor. If it were raised twice as high, how much potential energy would it have compared with what it had in the first case?

double

how did Galileo experiment work

dropped two objects with the same surface area/weight ratio off the leaning tower of Piza, fell at the same time and hiy the ground at the same time.

But the state of rest is only one form of equilibrium. An object moving at constant speed in a straight-line path is also in equilibrium. We say it's in

dynamic equilibrium

Quite interestingly, a falling object pulls upward on Earth with as much force as

earth pulls down on it

When findings in nature are expressed mathematically, they are

easier to verify or to disprove by experiment.

efficiecny formula

eficiency=usful energy output/total energy output

electrically splitting water into its constituent parts

electrolysis

Unlike most concepts in physics, friction is a very complicated phenomenon. The findings are __________ (gained from a wide range of experiments) and the predictions are ___________ (also based on experiment).

empirical; approximate

Whenever work is done,

energy is exchanged

cientific theories

evolve as they go through stages of redefinition and refinement.

Pseudoscience

fake science that pretends to be real science

3 types of friction

fluid, sliding, rolling

86.A heavy crate accidentally falls from a high

flying airplane just as it flies directly above Mike's shiny red Corvette defensively parked in a car lot. Relative to the Corvette, where does the crate crash?-86. It lands behind it because the plane is moving. Horizontal motion is independent of vertical and not change in motion happens in horizontal motion if neglecting air resistance. This means that when the object falls it speeds up going down from vertica motion but keeps going the direction of the plan horizontally.

97.If a flight mechanic drops a box of tools from a high

flying jumbo jet, it crashes to Earth. If an astronaut in an orbiting space vehicle drops a box of tools, does it crash to Earth also? Defend your answer.- GET CLEARANCE

Isaac Newton was the first to realize the connection between

force and mass in producing acceleration, which is one of the most central rules of nature.

Intensity=1/distance^2

formula for inverse square law

F=Gm1m2/d^2

formula for universal gravitation law

55. Boxes of various masses are on a friction

free level table. (a) Rank, from greatest to least, the net forces on the boxes. (b) Rank, from greatest to least, the accelerations of the boxes.-a. D, A = B = C b. A = C, B = D

fluid friction

friction that occurs as an object moves through a fluid (including air)

rolling friction

friction that occurs when an object rolls over a surface

sliding friction

friction that occurs when one solid surface slides across another

The point of support on which a lever rotates

fulcrum

aristotle didn't understand the

fundementals

in science, a fact is

generally a close agreement by competent observers who make a series of observations about the same phenomenon.

The potential energy due to elevated positions is called

gravtational potential energy

The greater the impulse exerted on something

greater its change in momentum

The equations are

guides to thinking that show the connections between concepts in nature.

126.A communications satellite with a 24

h period hovers over a fixed point on Earth. Why is it placed in orbit only in the plane of Earth's equator? (Hint: Think of the satellite's orbit as a ring around Earth.)-126. This will allow the satellite to be able to cover the biggest distance around the Earth. If it was placed more northern or southern, it won't go as far because it will just circle around it in the shape a ring would be on a finger.

Is the speed gained by ball B going down the extra dip the same as the speed it loses going up near the right

hand end and doesn't this mean that the speeds of balls A and B will be the same at the ends of both tracks?- Yes it will because both dips are the same height which means they will have the same downward and upward force. B is also losing speed from gravity when going up the hill so it will return to the speed of only one boost just like A. In conclusion, yes they will both be exiting at the same speed.

44.A different scaffold that weighs 400 N supports two painters, one weighing 500 N and the other weighing 400 N. The reading in the left

hand scale is 800 N. What is the reading in the right-hand scale?-500N

Galileo couldn't say why all bodies fall equally because

he never connected the concepts he developed—acceleration and inertia—with force.

29.What is the ultimate source of geothermal energy?

heat down in the earth

altitudes

heights above the ground

Four hundred years ago, people had difficulty with ideas like these. One reason is that

hey didn't yet travel in high-speed vehicles. Rather, they experienced slow, bumpy rides in horse-drawn carts.

This pair of forces, your pull on the cart and the cart's pull on you, make up the single interaction between you and the cart. Such observations led Newton to

his 3rd law of motion

When Galileo allegedly dropped objects of different weights from the Leaning Tower of Pisa, they didn't actually

hit at the same time

Chemistry builds on physics by telling us

how matter is put together, how atoms combine to form molecules, and how the molecules combine to make the materials around us.

86.You're in a car traveling on a highway at some specified speed limit. You see another car moving at the same speed directly toward you. How fast is the car approaching you, compared with the speed limit?

however fast the speed limit says because from it's veiw, it is travelling as fast as you are, and you are traveling ask fast as the speed limit says for you to be.

Solar power is seasonal in most parts of the world, which suggests a need for long-term seasonal storage in a medium such as

hyrdrogen

100% of the work input appeared as work output. would operate at 100% efficiency

ideal machine

14.Cite an example in which a force is exerted on an object without doing work on the object.

impossible

Interestingly, an object under the influence of only one force cannot be

in static or dynamic equalibrium

124.Railroad cars are loosely coupled so that there is a noticeable delay between the time the first car is moved and the time the last car is moved from rest by the locomotive. Discuss the advisability of this loose coupling and slack between cars from the point of view of impulse and momentum.

increases time of impulse

equation for , conservation of energy for machines

input force×input distance=output force×output distance.

speed at any instant

instantaneous speed

surface area to weight ratio is _______ proportional

inversely

9.What does it mean to say that momentum (or any quantity) is conserved?

it cannot be created or destroyed

the unit of work is the newton-meter (N⋅m),◂...▸(N⁣⋅⁣m)⁣, also called the

joule J

unit for power

joule per second or watt

22.What will be the kinetic energy of the ram of a pile driver when it suddenly undergoes a 10

kJ decrease in potential energy?-same

41.A 120

kg astronaut recedes from her spacecraft by activating a small propulsion unit attached to her back. The force generated by a spurt from this device is 30 N. Show that her acceleration is 0.25 m/s2.- a=Fnet/m=30 N/120 kg=0.25m/s2

65.What is the net force acting on a 1

kg ball in free fall? What is the net force if it encounters 2 N of air resistance?- The net force is mg, 10 N (or more precisely, 9.8 N). With air resistance the net force is 10 N − 2 N = 8 N (or more precisely 9.8 N − 2 N = 7.8 N).

57.Consider a 100

kg box of tools in the locations A, B, and C. (a) Rank, from greatest to least, the masses of the 100-kg box of tools. (b) Rank, from greatest to least, the weights of the 100-kg box of tools.-a. A = B = C b. C, A, B

36.In this chapter we learn that the cause of acceleration is given by Newton's second law: a=Fnetm. Show that the acceleration in Problem 35 results from a net force of 15 N exerted on a 3.0

kg cart. (Note: The unit N/kg is equivalent to m/s2.)-5m/s/s=15N/13kg

68.Which has more mass: a 2

kg fluffy pillow or a 3-kg small piece of iron? Which has more volume? Why are your answers different?- The 3 kg small piece of iron has more mass, while the 2 kg king sized pillow has more volume. The reason these two answers are the way they are is because mass is not the same as volume. Volume is just how much space an item takes up, while mass is the amount of matter in an object. The piece of iron has more mass because unlike the pillow, it is more solid, making it have more matter inside of it, while a pillow is not very solid. It rather has multiple pieces inside of it, so it has less matter. Meanwhile, a pillow has more volume because it is bigger or takes up more space than the small piece of iron. Size is not indicative of mass. The small peaice of iron has more atoms. COmpressed into small peice

71.Gravitational force on the Moon is merely ⅙ the gravitational force on Earth. What would be the weight of a 10

kg object on the Moon and on Earth? What would its mass be on the Moon and on Earth?- 4.55 on Earth, 0.77 on the Moon. It would be 10 kg on Earth and on the moon because unlike gravity, mass never changes because the amount of matter something has never changes. The weight of a 10-kg object on Earth is about 100 N, and on the Moon 1/6 of this, or nearly 17 N. The mass would be 10 kg on the Moon, Earth, or any location.

37.Knowing that a 1

kg object weighs 10 N, confirm that the acceleration of a 1-kg stone in free fall is 10 m/s2.- a=Fnet/m=10 N/1 kg=10 N/kg=10 m/s2

38.A simple rearrangement of Newton's second law gives Fnet = ma. Show that a net force of 84 N exerted on a 12

kg package is needed to produce an acceleration of 7.0 m/s2. (Note: The units kg·m/s2 and N are equivalent.)- 84N=12kg*7m/s/s

63.Is the gravitational force greater on a 1

kg piece of iron or on a 1-kg piece of glass? Defend your answer.-The force of gravity is the same on each because the masses are the same, as Newton's equation for gravitational force verifies.

46.Calculate the horizontal force that must be applied to a 1

kg puck for it to accelerate on a horizontal friction-free air table with the same acceleration it would have if it were dropped and fell freely.- 10N

15.Which requires more work: lifting a 50

kg sack a vertical distance of 2 m or lifting a 25-kg sack a vertical distance of 4 m?-same

48.For 3.0 s, Allison exerts a net force of 10.0 N on a 6.7

kg shopping cart that was initially at rest. Find the acceleration of the cart, and show that it moves a distance of 6.7 m.- 0.7m/s/s

118.Two facts: A freely falling object at Earth's surface drops vertically 5 m in 1 s. Earth's curvature "drops" 5 m for each 8

km tangent. Discuss how these two facts are related to the 8-km/s orbital speed necessary to orbit Earth.-118. If in 1s of free fall of an object it drops 5m, and Earth's curvature drops 5m for every 8 km, that means that for every 8 kilometers traveled in 1 second, Earth's curvature drops 5m. If an object was in free fall, for every second, it would drop 5 meters, and for an object in orbit, for every 8 km traveled, Earth's curvature drops by 5 meters, so if every second 8 kilometers would be traveled across Earth in space, you would be going in a circle around Earth if you were in free fall.

If the change in momentum occurs over a short time, then the hitting force is

large

Newton's first law of motion, usually called the

law of inertia,

107.Two balls, A and B, are released simultaneously from rest at the left end of the equal

length tracks A and B, as shown. Which ball, A or B, will reach the end of its track first?- Ball B reaches the end of its track first, for its average speed along the lower part as well as the sloped parts is greater than the average speed of the ball A along the straighter track A.

lighter

less speed. easier to get going

The study of science today branches into the study of living things and nonliving things:

life science and physical science

106.If you toss a coin straight upward while riding in a train that travels at uniform and steady motion along a straight

line track, where does the coin land? Where does the coin land if the train slows while it is tossed? Where does it land if the train rounds a curve?-It will land in the palm of your hand because it is already moving as fast as the train and so are you. When you toss it in the air, it is like a plane moving upwards and downwards while moving. From a still frame of reference the coin is like the plane compared to it, but compared to you, it is only moving up then down. If the train slows down the coin will land in front of you because it is still moving at a high speed and is still moving in mid air, so when the train stops it you will see it has been moving and it will stop moving afterwards because unlike you, the train is not touching it. If the train turns then the coin will land in the direction opposite of where the train turned because it is moving straight and the train is turning. Horizantal an Vertical are independent of each other. Newton's first law of inertia-all motion is relative

123.Imagine that you're in a completely dark room with no windows except a 1 ft2 round hole in the roof. When the Sun is high in the sky, about 100 W of solar power enters the hole. On the floor where the light hits, you place a beach ball covered with aluminum foil, with the shiny side out. Discuss the illumination in your room compared with that of a 100 W incandescent light bulb.

llumination by each would be much the same, 100 W.

Aristotle used ________ to establish his ideas of motion, whereas Galileo used ___________.

logic; experiment

72.A small light source located 1 m in front of a 1

m2 opening illuminates a wall behind. If the wall is 1 m behind the opening (2 m from the light source), the illuminated area covers 4 m2. How many square meters are illuminated if the wall is 3 m from the light source? 5 m from the light source? 10 m from the light source?-72. It is 9 m^2 because the inverse square law's formula's distance is squared. In this case, 3m^2 is 9m. The next one 25m^2 because the inverse square law's formula's distance is squared. In this case, 5m^2 is 25m. The final one is 100 m^2 because the inverse square law's formula's distance is squared. In this case 10m^2 is 100m.

116.Two equal

mass blocks are connected by a length of string. One block is placed at rest on a very smooth table, and the other block dangles off the table's edge. You hold the blocks so they don't move. When released, the hanging one accelerates downward, pulling the top block horizontally across the table. Why do both blocks undergo the same amount of acceleration? Show that this acceleration ideally is one-half g.-

104.In the 2014 Rosetta mission, when a probe from Earth landed on the low

mass comet, the probe bounced. Why were scientists overseeing the mission concerned about the comet's escape speed?-104. Escape speed is the speed needed to escape the pull of gravity of something. In this case, if the probe goes above the comet's escape speed, it will just bounce off the comet as witnessed. If they had lowered the speed coming in, the probe would have had no problems landing on the comet.

before the advent of Islam, Arab nations developed

mathematics and learned about the production of glass, paper, metals, and various chemicals.

Biology is more complex than physical science, for it involves

matter that is alive.

When the net force on something is zero, we say that the object is in

mechanical equalibrium

Chemists speak of the theory of

metallic bonding in metals,

m stands for

meters

The life sciences branch into such areas as

molecular biology, microbiology, and ecology.

mass is

more fundamental than weight; it is a fundamental quantity that completely escapes the notice of most people.

27.What becomes of energy when efficiency is lowered in a machine?

more is used

hevaier

more speed harder to get going.

When we lift a load against Earth's gravity, work is done. The heavier the load or the higher we lift the load

more work being done

Physics is the study of such concepts as

motion, force, energy, matter, heat, sound, light, and the components of atoms.

Galileo was concerned with how things

move rather than why they move

3.Why is it a good idea to extend your bare hand forward when you are getting ready to catch a fast

moving baseball?-To decrease the time of impulse. This will cause the momentum to decrease drastically faster.

Which has greater momentum: an automobile at rest or a moving skateboard?

moving skateboard

net force equiblibrium rule

must have 0 net force to be in equilibirum because the main forces acting on something cancel each other out

Science is the present-day equivalent of what used to be called

natural philopsophy

Most often, air resistance is not

negligible for falling objects.

Which exerts the force and which receives the force? Isaac Newton's answer to this was that

neither force has to be identified as "exerter" or "receiver," and he concluded that both objects must be treated equally.

hen we say "force," we imply the total force, or __________, acting on an object.

net force

Is there one scientific method?

no

Scientists use the word theory in a way that differs from its usage in everyday speech. In everyday speech, a theory is

no different from a hypothesis—a supposition that has not been verified.

a truck at rest has

no momentum at all.

Whenever energy is transformed or transferred

none is lost and none is gained

This upward support force, often called the

normal force

there is no way that an object can exert a force on

nothing

While art broadens our understanding

of ourselves

87.Two people of equal mass attempt a tug

of-war with a 12-m rope while standing on frictionless ice. When they pull on the rope, each person slides toward the other. How do their accelerations compare, and how far does each person slide before they meet?-The forces on each are the same in magnitude, and their masses are the same, so their accelerations will be the same. They will slide equal distances of 6 meters to meet at the midpoint.

89.Which team wins in a tug

of-war: the team that pulls harder on the rope, or the team that pushes harder against the ground? Explain.- The winning team pushes harder against the ground. The ground then pushes harder on them, producing a net force in their favor.

86.If a Mack truck and a motorcycle have a head

on collision, upon which vehicle is the impact force greater? Which vehicle undergoes the greater change in its motion? Defend your answers.- They will have equal impact fporce because of NEwton's 3rd law. The motorcycle will have a greater cahnge in accelration because the truck has a lot more mass than the motorcycle (Newton's 2nd law and NEwton's 1st LAw)

inversely proportional

one goes up other goes down

directly proportional

one goes up other goes up

Again, for emphasis: friction always acts in a direction to _________ motion.

oppose

science broadens our understanding of

our envirment

An interaction requires a _______ of forces acting on _________ objects

pair; two

---------> ^ |

perpendicular net force

The arts are concerned with

personal interpretation and creative expression.

The physical sciences branch into such areas as

physics, chemistry, the Earth sciences, and astronomy.

Any substance that can do work through chemical action posseses

potential energy

The chemical energy in fuels is also

potential energy

106.When a driver applies the brakes to keep a car going downhill at constant speed and constant kinetic energy, the potential energy of the car decreases. Where does this energy go? Where does most of it appear in a hybrid vehicle?

potential energy turns into heat and kinetic turns to entropy Hybrid changes braking power and potrntial energy into electric energy

19.What is the relationship between work and power?

power is the rate of change of work

formula for power

power=work done/time

115.A friend claims that bullets fired by some high

powered rifles travel for many meters in a straight-line path before they start to fall. Another friend disputes this claim and states that all bullets from any rifle drop beneath a straight-line path a vertical distance given by 1/2 gt2 as soon as they leave the barrel and that the curved path is apparent for low velocities and less apparent for high velocities. Now it's your turn: Do all bullets drop the same vertical distance in equal times? Explain.-For very slow-moving bullets, the dropping distance is comparable to the horizontal range, and the resulting parabola is easily noticed (the curved path of a bullet tossed sideways by hand, for example). For high speed bullets, the same drop occurs in the same time, but the horizontal distance traveled is so large that the trajectory is "stretched out" and hardly seems to curve at all. But it does curve. All bullets will drop equal distances in equal times, whatever their speed. (It is interesting to note that air resistance plays only a small role, since the air resistance acting downward is practically the same for a slow-moving or fast-moving bullet.)

It was his experiments with _______ that first made him famous.

prisms

Claims that are presented as scientific but do not meet these standards are what we call

pseudoscience, which literally means "fake science."

so if the speed of an object is doubled, its kinetic energy is

quadrupled

Physicists, for example, speak of the

quark theory of the atomic nucleus,

Power is also the

rate at which energy is changed from one form to another.

If action is A acting on B

reaction is B acting on A

When a skydiver steps from a high-flying plane, the air resistance on the skydiver's body builds up as the falling speed increases. The result is

reduced acceleration. The acceleration can be reduced further by increasing frontal area.

all motion is

relative

Many people are troubled about not knowing the answers to

religious and philosophical questions. Some avoid uncertainty by uncritically accepting almost any comforting answer.

11.Railroad car A rolls at a certain speed and makes a perfectly elastic collision with car B of the same mass. After the collision, car A is observed to be at rest. How does the speed of car B compare with the initial speed of car A?

same

12.If the equally massive railroad cars of Question 11 couple together after colliding inelastically, how does their speed after the collision compare with the initial speed of car A?

same

As the answers to natural philosophy were found, they became part of what is now called

science

A hypothesis that is capable of being prove right but not capable of being proved wrong is not

scientific hypothesis

Newtons connection between these two things was expressed in his

second law of motion

122.Occupants inside future donut

shaped rotating habitats in space will be pressed to their floors by rotational effects. Their sensation of weight feels as real as that due to gravity. Does this indicate that weight need not be related to gravity?-122. This does not. This is because weight is felt from gravity pushing down on you and a support force is pushing up on you. The support force is what you feel and because of Newton's 3rd law, you are feeling your own weight. In this case, the rotational station spins around and acts like a zero gravity ride in a carnaval. It provides a support force that pushes on your feet, which keeps them firmly on the ground because it is moving so fast to the point where it pushes you around. You are just feeling a force push on you really hard and that is what gives the illusion of Earth's gravity in a low gravity environment.

E (sideways M)means

sigma

a fast car can have more momentum than a

slow truck

Consider the interesting demonstration of the falling coin and feather in the glass tube (Figure 2.13). When air is inside, we see that the feather falls more ___________ due to air resistance. The feather's weight is very small, so it reaches terminal speed _________.

slowly; quickly

42.Henry Heavyweight weighs 1200 N and stands on a pair of bathroom scales in such a way that one scale reads twice as much as the other. What are the scale readings?

smaller one:400N bigger one: 800 N

Friction occurs for

solids liquids and gases

electric feild

space about an electrically charged object is energized with an

Any combination of units for distance and time can be used for

speed

Moving things often have variations in

speed

Air resistance depends primarily on two things:

speed and frontal area

105.Because Earth rotates once every 24 hours, the west wall in your room moves in a direction toward you at a linear speed that is probably more than 1000 km per hour (the exact speed depends on your latitude). When you stand facing the wall, you are carried along at the same speed, so you don't notice it. But when you jump upward, with your feet no longer in contact with the floor, why doesn't the high

speed wall slam into you?- When you jump, your horizontal motion matches that of Earth, and no force acts on you to change that. Hence, you travel along with Earth.

When an object remains stationary, the forces on it add up to zero—it's in equilibrium. More specifically, we say it's in

static equalibrium

Constant speed means

steady speed, neither speeding up nor slowing down.

Friction is due to tiny surface bumps and also to the ________ of the atoms on the surfaces of the two materials

stickiness

71.Why does a cat that falls from the top of a 50

story building hit a safety net below no faster than it would if it fell from the 20th story?-The terminal speed attained by the falling cat is the same whether it falls from 50 stories or 20 stories. Once terminal speed is reached, falling extra distance does not affect the speed. (The low terminal velocities of small creatures enable them to fall without harm from heights that would kill larger creatures.)

Constant direction is a

straight line—the object's path doesn't curve.

matter is _____________, and energy is the _________________

substance; mover of the substance

Except for nuclear power, practically all our energy is derived from

sun

velocity is inversely proportional to

surface area

A scientific theory, on the other hand, is

synthesis of a large body of information that encompasses well-tested and verified hypotheses about certain aspects of the natural world.

Only an impulse external to a system can change the momentum of a

system

122.What is the fuel that powers a fuel cell in forklifts, busses, and trains?

takes hydrogen and oxygen and uses energy to combine them into water and uses electricity to turn that into energy

Galileo was one of the first to build a _________, and the first to direct it to the ___________ ___________ and discover mountains on the _______ and the moons of __________.

telescope; nightime sky; Moon; Juptier

Terminal speed in a given direction (often downward).

terminal velocity

The 16th-century Polish astronomer Nicolaus Copernicus caused great controversy when he published a book proposing that

the Sun is stationary and that Earth revolves around the Sun

Science

the collective findings of humans about nature, and a process of gathering and organizing knowledge about nature.

average speed is

the entire distance covered divided by the total time travelled

he fact that the net force on the desk equals zero means that

the force of friction must be equal in magnitude and act opposite to our pushing force.

Note that a satellite in circular orbit is always moving in a direction perpendicular to

the force of gravity that acts upon it.

tention

the force that is transmitted through a rope, string or wire when pulled by forces acting from opposite sides.

For a suspended object at rest, like the bag of flour, the rule states that

the forces acting upward on the body must be balanced by other forces acting downward to make the vector sum equal zero. (

what would a police offucer be comparing your car to when using a speed taker thing

the ground

terminal velocity

the point at whih the downard force of air resistance equal each other. Object will not accelrate (equilibirum). Max accleration in air or on road as fast as you can go.

When direction doesn't change, acceleration may be expressed as

the rate at which speed changes

the introduction of gunpowder changed

the social and political structure of Europe in the 14th century.

Religion addresses

the source, purpose, and meaning of it all.

magnetic feild

the space around a magnet is energized with

We see that the distance of free fall from rest is directly proportional to

the square of the time of fall

In the absence of work input or output or other energy exchanges,

the total energy of a system before some process or event is equal to the total energy after.

a process that releases radiant energy, a small part of which reaches Earth

thermonuclear fusuion

Statement to be memorized

these things go hand in hand with each other: zero accelration, equilibium, constant velocity, zero net force

the greater the force of attraction between them, in direct proportion to the masses.

thus, the greater the masses m1 and m2,

Speed is inversely proportional to

time

yet

to-be-discovered particles of exotic dark matter.-Another 23% is composed of the

Formula for average speed

total distance/total time= average speed

79.In the 2014 Rosetta mission, a probe from Earth landed on a comet of very low mass. If the probe had been twice as massive, how would its weight on the comet surface have been affected?

ts weight, although very small, would be twice.

Every contact requires at least a

twoness

129.(Here's a Chapter 4

type question): The first stage of each SpaceX rocket that services the ISS no longer is dumped into the sea, but is returned for recycling (when all goes well). As the empty first stage falls back to Earth, one of its main engines slows its descent velocity to zero at the moment of touchdown. Is it correct to say that during this maneuver, the velocity and the acceleration of the first stage are in opposite directions? Defend your answer.-That is correct. Like the car that slows when acceleration is opposite its velocity, the descending first stage of the SpaceX rocket accelerates upward while its velocity is downward, ultimately reducing to a timely zero velocity.

128.(Here's a Chapter 2

type question): When the brakes are applied on a vehicle moving to the right, the horizontal net force on the vehicle is to the left. A friend says that the velocity and acceleration of the vehicle are in opposite directions. Do you agree or disagree? Defend your answer.-128. Yes I do agree. If the horizontal net force is on the left pushing against the already moving force on the right, the velocity pushing on the right must decelerate or accelerate to the left to change the direction. This will happen because the forces pushing left are bigger than the forces pushing right. So if the vehicle's velocity was 10m/s and the acceleration is -5m/s/s, then it would go 10m/s, 5m/s, 0m/s (still). It could go in reverse, but in this case, only the brakes are applied so there is no need to go into the negatives.

When the ideas of science are expressed in mathematical terms, they are

unabiguous

Natural philosophy was the study of

unanswered questions about nature

An important message in science, however, is that

uncertainty is acceptable

The combination of energy and matter makes up the

universe

Velocity is a

vector quantity

EF=

vector sum of forces

When straight-line motion is being considered, we can use the words __________ and _________ interchangeably in the definition of acceleration

velocity

factors of fluid friction

viscosity- how hard it is to go through something speed- how fast someting is going surface- shape of something or what something is made of

mg stand for

weight

velocity is directly proportional to

weight

frame of reference

what we compare moving objects to

the ellipse is a circle. So we can see that a circle is a special case of an ellipse.

when both foci are together

13.When is energy most evident?

when we do work

Although Galileo founded the concepts of both inertia and acceleration and was the first to measure the acceleration of falling objects, he was unable to explain

why objects of various masses fall with equal accelerations.

This exhilarating sport, __________, goes beyond what flying squirrels can accomplish, since a flyer can achieve horizontal speeds appreciably greater than 170 km/h (100 mph).

wingsuit flying

. Internal forces and impulses

wont work

formula for work energy theorum

work equals= change in kinetic energy

work input=

work output

20.What is the relationship between the gain in kinetic energy and the work when work is done?

work=change in kinetic energy

24.Can a machine multiply input force? Input distance? Input energy? (If your three answers are the same, seek help, because this is an important question.)

yes yes no

if action and reaction forces are equal and opposite, why don't they cancel to zero?

you cant cancel the fprce pn one thing with a force on the other

newtons third law simplified

you cant touch without being touched

When you jump from an elevated position down to the ground, what happens if you keep your legs straight and stiff? Ouch! Instead, you bend your knees when your feet make contact with the ground. By doing so you

you extend the time during which your momentum decreases to 10 to 20 times that of a stiff-legged, abrupt landing

Two things enter the picture whenever work is done:

(1) application of a force and (2) the movement of something by that force.

Formula for the conservation of momentum

(net mv)before=(net mv)after

constant speed.

no component of force to pull it forward or backward, and the ball rolls at

When you step on a bathroom scale, you effectively compress a spring inside. When the pointer stops, the elastic force of the deformed spring balances the gravitational attraction between you and Earth

nothing moves, because you and the scale are in static equilibrium.

For any system in which all forces are internal—as, for example, cars colliding, atomic nuclei undergoing radioactive decay, or stars exploding—the net momentum of the system before and after the event is

same

With the aid of high

speed computers, the answers to these questions are used to find a new path. Corrective thrusters direct the rocket to this new path. This process is repeated all the way to the goal.*-it is interesting to note that the accuracy with which an unoccupied rocket reaches its destination is not accomplished by staying on a planned path or by getting back on that path if the rocket strays off course. No attempt is made to return the rocket to its original path. Instead, the control center in effect asks, "Where is it now and what is its velocity? What is the best way to reach its desti-nation, given its present situation?"

11.2 km/s

the escape speed from the surface of Earth.**

But if the time is short,

the fprce is large

Remember that for an object brought to rest,

the impulse is the same no matter how it is stopped

Whenever objects collide in the absence of external forces,

the net momentum of both objects before the collision equals the net momentum of both objects after the collision.

. In the case of hitting either the wall or the haystack and coming to a stop, it takes

the same impulse to decrease your momentum to zero.

A moving truck has more momentum than a car moving at the same speed because

the truck has more mass.

If the mass remains unchanged, as is most often the case,

the velocity changes and acceleration occurs