Physics
What is the acceleration of a car that maintains a constant velocity of 100 km/h for 10 s?
0 km/h·s
An object covers a distance of 8 meters in the first second of travel, another 8 meters during the next second, and 8 meters again during the third second. Its acceleration is
0 m/s2.
An ostrich egg of mass m is tossed at a speed v into a sagging bed sheet and is brought to rest in a time t. 1.) Find the force acting on the egg when it hits the sheet. 2.) If the mass of the egg is 1.4 kg , its initial speed is 2.5 m/s , and the time to stop is 0.20 s, find the average force on the egg.
1.) F = mv/t 2.) F = 18 N
Suppose a ball of putty moving horizontally with 1 kg·m/s of momentum collides with and sticks to an identical ball of putty moving vertically with 1 kg·m/s of momentum. What is the magnitude of their combined momentum?
1.41 kg·m/s
In the preceding question, what is the total momentum of the balls of putty before and after the collision?
1.41 kg·m/s before and after.
What is the net force that acts on a 1-kg freely falling object?
10 N
What is the weight of a 1-kilogram brick resting on a table?
10 N
The force of friction on a sliding object is 10 N. The applied force needed to maintain a constant velocity is
10 N.
What will the kinetic energy of a pile driver ram be if it starts from rest and undergoes a 10 kJ decrease in potential energy?
10 kJ
What is the acceleration of a car moving along a straight road that increases its speed from 0 to 100 km/h in 10 s?
10 km/h·s
Given the measurements 10 m, 10 m/s, and 10 m/s2, which is a measure of speed, which is a measure of distance, and which is a measure of acceleration?
10 m is distance, 10 m/s is speed, and 10 m/s2 is acceleration.
What is the net force acting on a 1-kg ball in free fall?
10.0 N
One end of a rope is pulled with 100 N, while the opposite end also is pulled with 100 N. The tension in the rope is
100 N.
A river 100 m wide flows due south. A boat that goes 1 m/s relative to the water is pointed due east as it crosses from the west bank. The boat crosses in
100 s.
What is the efficiency of a machine that miraculously converts all the input energy to useful output energy?
100%
How far does a horse travel if it gallops at an average speed of 25 km/h for 30 min?
12.5 km
What is the speed over the ground of an airplane flying at 100 km/h relative to the air caught in a 100-km/h right-angle crosswind?
141 km/h
Consider a book that weighs 15 N at rest on a flat table. How many newtons of support force does the table exert on the book?
15 newtons up
A force of 50 N is applied to the end of a lever, which is moved a certain distance. If the other end of the lever moves one-third as far, how much force does it exert?
150 N
The power expended doing 100 J of work in 50 s is
2 W.
What is the average speed in kilometers per hour of a horse that gallops a distance of 15 km in a time of 30 min?
30 km/h
If you push a crate horizontally with 100 N across a 10-m factory floor and the friction between the crate and the floor is a steady 70 N, how much kinetic energy does the crate gain?
300 J
When a karate chop breaks a board with a 3000-N blow, the amount of force that acts on the hand is
3000 N.
Burl and Paul have a total weight of 1300 N. The tensions in the supporting ropes that support their scaffold add to 1700 N. The weight of the scaffold itself must be
400 N.
One half second after starting from rest, a freely falling object will have a speed of about
5 m/s.
The resultant of a 40-N force at right angles to a 30-N force is
50 N.
A toy elevator is raised from the ground floor to the second floor in 20 seconds. The power needed using 1000 J of work, is
50 W.
Part complete If a car increases its velocity from zero to 60 m/s in 10 seconds, its acceleration is
6 m/s2.
If an input of 100 J in a pulley system increases the potential energy of a load by 60 J, what is the efficiency of the system?
60%
Part complete What is the net force acting on a falling 1-kg ball if it encounters 2 N of air resistance?
8.00 N
In the preceding question, which case requires the greatest impulse?
A baseball that is caught and then thrown back
Which undergoes the greatest change in momentum (if all of the baseballs have the same speed just before being caught and just after being thrown)?
A baseball that is caught and then thrown back
Why do we say that force is a vector quantity?
A force has a magnitude and a direction.
What is meant by the term vector resolution?
A vector can be broken into two components at right angles that add together to make the original vector.
When are you most aware of your motion in a moving vehicle: when it is moving steadily in a straight line or when it is accelerating? If you were in a car that moved with absolutely constant velocity (no bumps at all), would you be aware of the motion?
Accelerating. You would not be aware of the motion if you did not look outside the car.
How does acceleration depend on mass?
Acceleration is inversely proportional to mass.
State Newton's second law of motion.
Acceleration is proportional to net force and inversely proportional to mass.
How does acceleration depend on the net force?
Acceleration is proportional to the net force.
What is the effect of air resistance on the acceleration of falling objects?
Air resistance decreases the acceleration of falling objects.
What exactly is meant by a "freely falling" object?
An object in free fall falls under gravity alone with no friction.
What does it mean to say something is in mechanical equilibrium?
An object in mechanical equilibrium experiences a zero net force.
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?
Both take the same 1000 J.
What two units of measurement are necessary for describing speed?
Distance and time
If a machine multiplies force by a factor of 4, what other quantity is diminished, and by how much?
Distance is diminished to one-quarter.
If a ball is projected upward from the ground with 10 kg • m/s of momentum, what is Earth's momentum of recoil? Why do we not feel this?
Earth's momentum of recoil is 10 units of momentum. We do not feel this because the earth has a lot of mass and it would have a small change in its velocity.
Exactly what is it that enables an object to do work?
Energy
If you stand next to a wall on a frictionless skateboard and push the wall with a force of 46 N , how hard does the wall push on you?
F = 46 N
How is the impulse -momentum relationship related to Newton's second law?
F=ma=mΔv/Δt, so Ft=Δ(mv)
Does fluid friction vary with speed?
Fluid friction increases as speed increases.
State Newton's third law of motion.
For every action there is an equal and opposite reaction.
What are the units for force?
Force can be expressed in newtons or pounds.
Can a machine multiply input force? Input distance? Input energy?
Force: Yes; Distance: Yes; Energy: No
What relationship between distance traveled and time did Galileo discover for freely falling objects released from rest?
Galileo discovered that distance increased as the time squared.
What did Galileo discover in his legendary experiment on the Leaning Tower of Pisa?
Galileo found that a heavier stone does not fall significantly faster than a lighter one.
Give an example of what it means to say mass and weight are proportional to each other?
If the mass doubles, then the weight doubles, too.
Part complete If you throw a ball horizontally while standing on roller skates, you roll backward with a momentum that matches that of the ball. Will you roll backward if you go through the motions of throwing the ball, but instead hold on to it? Explain. Assuming you've answered them in terms of momentum conservation, answer them also in terms of Newton's third law (or vice versa, if you answered already in terms of Newton's third law).
If there is no momentum then no oppositely directed momentum will be imparted to the thrower. There will be no recoil momentum gained by you. Throwing the ball will have no net affect. When you throw the ball you recoil backward a little, but at the end you stop moving.
Consider the system of a single football. If you kick it, is there a net force to accelerate the system? If a friend kicks it at the same time with an equal and opposite force, is there a net force to accelerate the system?
If you kick the football, there is a net force to accelerate the system; if you and your friend kick it, there is not.
An apple hanging from a limb has potential energy because of its height. If it falls, what becomes of this energy just before it hits the ground? When it hits the ground?
Immediately before hitting the ground the apple's energy is kinetic energy; when it hits the ground, its energy becomes thermal energy.
Distinguish between force and impulse.
Impulse is force times a time interval.
What did Galileo discover about moving bodies and force in his experiments with inclined planes?
In the absence of a retarding force, a body will keep moving at a constant speed in a straight line forever.
What is inertia?
Inertia is the tendency of a body to maintain its state of motion in the absence of applied forces.
Fill in the blanks: Newton's first law is often called the law of ____; Newton's second law is the law of ____; and Newton's third law is the law of ____.
Inertia, acceleration, action -reaction
What kind of speed is registered by an automobile speedometer?
Instantaneous speed
A bird sitting in a tree is traveling at 30 km/s relative to the faraway Sun. When the bird drops to the ground below, does it still move at 30 km/s, or does this speed become zero?
It continues to move at 30km/s relative to the Sun, but it has a speed of 0 km/s relative to the ground.
What type of path does a moving object follow in the absence of a force?
It continues to move in a straight line at a constant speed.
What is the distance fallen for a freely falling object 1 s after being dropped from a rest position? What is the distance for a 4-s drop?
It falls 5 m in 1 s and 80 m in 4 s.
What is the gain in speed per second for a freely falling object?
It gains approximately 10 m/s.
When the speed of a moving car is doubled, how much more kinetic energy does it have?
It has four times as much.
What is the acceleration of the ball when it is moving up, when it is at the maximum height, and when it is moving down? (Note: The acceleration graph is shown in red.)
It is always negative.
What is the value of the velocity of the ball when it reaches its maximum height?
It is always zero.
What is the force of friction acting on a shoe at rest on an incline compared with the resultant of the vectors mg and N?
It is equal and opposite.
When an object is thrown upward, how much speed does it lose each second (ignoring air resistance)?
It loses 10 m/s of speed each second until it reaches the high point, then it gains 10 m/s each second.
If a car is moving at 90 km/h and it rounds a corner, also at 90 km/h, does it maintain a constant speed? A constant velocity?
It maintains a constant speed, but does not maintain a constant velocity.
What does it mean to say that momentum is conserved?
It means momentum does not change.
Compared with a car moving at some original speed, how much work must the brakes of a car supply to stop a car that is moving twice as fast? How will the stopping distances compare?
It takes four times the work and four times the stopping distance.
A car is raised a certain distance in a service-station lift, thus giving it potential energy relative to the floor. If it were raised twice as high, how much more potential energy would it have?
It would have twice as much potential energy.
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?
Kinetic energy is the energy of motion and can be determined by KE = 1/2mv^2. So, the heavier object has less speed and the lighter object has more speed. It's the same with molecules, where the lighter ones move faster on the average than more massive ones.
If both sacks in the preceding question are lifted their respective distances in the same time, how does the power required for each compare? How about for the case in which the lighter sack is moved the same distance in half the time?
Lifted in the same time, the power is the same. The light sack moving in half the time requires double the power.
When you are struck by a moving object, is it favorable that the object makes contact with you over a short time or over a long time?
Long contact time decreases the magnitude of the average force and is favorable.
In the string-pull illustration in Figure 4.8, a sharp jerk on the bottom string results in the bottom string breaking. Does this occur because of the ball's weight or its mass?
Mass
Fill in the blanks: The Standard International unit for mass is _____. The Standard International unit for force is _____.
Mass is kilograms; force is newtons.
In which is momentum conserved: an elastic collision or an inelastic collision?
Momentum is conserved in elastic and inelastic collisions.
How does Newton's first law of motion relate to Galileo's concept of inertia?
Newton refined Galileo's concept of inertia and made it his first law of motion.
The impulse-momentum relationship is a direct result of
Newton's 2nd law.
Which of Newton's three laws focuses on interactions?
Newton's third law
Can you produce a net impulse on an automobile if you sit inside and push on the dashboard.
No, never.
Can you physically touch a person without that person touching you with the same amount of force?
No, when you touch a person, they must touch you with an equal and opposite force.
Since an object weighs less on the surface of the Moon than on Earth's surface, does it have less inertia on the Moon's surface?
No.
Can we correctly say that hydrogen is a new source of energy? Why or why not?
No. It takes energy to make hydrogen.
What is the ultimate source of geothermal energy?
Nuclear power in Earth's interior
What is the approximate weight of a quarter-pound hamburger after it is cooked?
One newton
If the forces that act on a cannonball and the recoiling cannon from which it is fired are equal in magnitude, why do the cannonball and cannon have very different accelerations?
Remember F = ma, and note that the cannon has a much greater mass than the cannon ball, so the cannon accelerates less for the same force.
What is recycled energy?
Reused energy that otherwise would be wasted
Why is it advantageous to roll with the punch in boxing?
Rolling with the punch increases contact time, which decreases the force.
Part complete Shake something to and fro and you're measuring its what? Lift it against gravity and you're measuring its what?
Shaking measures mass, whereas lifting measures weight.
How does speed affect the friction between a road and a skidding tire?
Speed has no effect on the friction.
Which is normally greater: static friction or sliding friction on the same object?
Static friction is normally greater than dynamic friction.
A different scaffold that weighs 400 N supports two painters, one 500 N and the other 400 N. The reading in the left scale is 800 N. What is the reading in the right-hand scale?
T = 500 N
Why does a heavy parachutist fall faster than a lighter parachutist who wears a parachute of the same size?
Terminal speed must be higher to make air drag equal the gravity force for a heavier person.
Does the International Space Station have gravitational PE? KE? Explain.
The International Space Station has both gravitational PE and KE. Gravitational PE is due to elevated positions. PE = mgh so gravitational PE has both weight and height which the space station both has. The space station is in orbit and is moving around earth and kinetic energy is the energy of motion. So, the space station has kinetic energy.
What is the ultimate source of the energy from fossil fuels, dams, and windmills?
The Sun
What is the acceleration of a falling object that has reached its terminal velocity?
The acceleration is 0.
How does the direction of acceleration compare with the direction of the net force that produces it?
The acceleration is in the direction of the net force.
If the mass of a sliding block is tripled while a constant net force is applied, by how much does the acceleration change?
The acceleration is reduced to 1/3 of its original value.
How does the magnitude of acceleration of the rifle compare with the magnitude of acceleration of the bullet, and why?
The acceleration of the rifle is smaller than the acceleration of the bullet. They experience the same magnitude of force, but the mass of the rifle is greater, and so the rifle will experience a smaller acceleration than the bullet.
If the mass of a sliding block is somehow tripled at the same time the net force on it is tripled, how does the resulting acceleration compare with the original acceleration?
The acceleration remains the same.
If the net force acting on a sliding block is somehow tripled, what happens to the acceleration?
The acceleration triples.
In terms of impulse and momentum, why do air bags in cars reduce the chances of injury in accidents?
The air bags in the car increases the time the force is applied. It decreases the force. The result will be a lesser force for a longer duration.
Why is a force that is applied for a short time more effective in karate?
The average force is increased.
What did Galileo discover about the amount of speed a ball gained each second when rolling down an inclined plane? What did this say about the ball's acceleration?
The ball had constant acceleration, so it gained the same speed every second.
Which exerts the greater impulse on a steel plate- machine gun bullets that bounce from the plate, or the same bullets squashing and sticking to the plate?
The bouncing bullets. When you reverse direction then there is a larger impulse and a greater momentum.
A boxer can hit a heavy bag with great force. Why can't he hit a piece of tissue paper in midair with the same amount of force?
The boxer can only hit the tissue paper with a force as large as the tissue paper can exert on the boxer, and the low-mass tissue can only exert a weak force.
How does the distance traveled by the bullet compare with the distance traveled by the rifle in the same time, and why?
The bullet will travel farther than the rifle because it has a greater magnitude of acceleration.
According to the parallelogram rule, what quantity is represented by the diagonal of a constructed parallelogram?
The diagonal is the resultant, or sum, of two vectors.
If two objects of the same size move through the air at different speeds, which encounters the greater air resistance?
The faster object encounters more air resistance.
What two principal factors affect the force of air resistance on a falling object?
The force depends mostly on frontal area and speed.
For the same force, why does a long cannon impart more speed to a cannonball than a short cannon?
The force is applied for a longer time in the long cannon.
How does the force of friction for a sliding object vary with speed?
The force of friction is approximately independent of speed.
As you increase your push on a stationary crate, will friction on the crate increase also?
The friction force increases and is opposite in direction to your push.
When you push horizontally on a crate that doesn't slide on a level floor, how great is the force of friction on the crate?
The friction force is equal and opposite to your push.
If you push on a crate with a horizontal force of 100 N and it slides at constant velocity, what is the magnitude and direction of the frictional force acting on the crate?
The frictional force on the crate is 100 N opposite the direction of motion.
How does a helicopter get its lifting force?
The helicopter exerts downward forces on air; the reaction forces of the air on the helicopter are upward and called lift.
Your friend says that the law of momentum conservation is violated when a ball rolls down a hill and gains momentum. What do you say?
The law of momentum says that if there is no external force acting on the system then the momentum will not change at all. This is not a violation of the law because of gravity acting on the ball. Gravity is an external force.
How does the force on the rifle compare with the force on the bullet, and why?
The magnitude of the force of the rifle is equal to the magnitude of force on the bullet and the forces are in the opposite direction, because for every action there is an equal and opposite reaction.
What happens to the magnitude of the normal vector on a block resting on an incline when the angle of the incline increases?
The magnitude of the normal vector decreases.
Which has a greater momentum: a heavy truck at rest or a moving skateboard?
The moving skateboard.
What is the net force on a cart that is pulled to the right with 100 pounds of force and to the left with 30 pounds of force?
The net force is 70 pounds to the right.
If the system is considered to be the apple and the orange together, is there a net force on the system when the apple pulls (ignoring friction with the floor)?
The net force is zero because the action and reaction forces are equal and opposite.
What is the net force on a bag pulled down by gravity with a force of 18 newtons and pulled upward by a rope with a force of 18 newtons?
The net force is zero newtons.
What is the net force on an object that is pulled with forces of 80 newtons to the right and 80 newtons to the left?
The net force is zero newtons.
What is the net force on an object in either static or dynamic equilibrium?
The net force is zero.
What is the net force that acts on a 10-N falling object when it encounters 4 N of air resistance? When it encounters10 N of air resistance?
The net forces are 6 N and 0 N, respectively.
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? Assuming you've answered them in terms of momentum conservation, answer them also in terms of Newton's third law (or vice versa, if you answered already in terms of Newton's third law).
The only way the person can get to shore is if he would take off his clothes and would have to throw them the opposite way. The person will move in the opposite direction on the friction less ice according to conservation of momentum. So for every action, there is an equal and opposite reaction according to Newton's third law.
Part complete The ratio circumference/diameter for all circles is π. What is the ratio force/mass for freely falling bodies?
The ratio is g.
Why doesn't a heavy object accelerate more than a light object when both are freely falling?
The ratio of the weight to mass is the same for all objects in the same locality.
Consider hitting a baseball with a bat. If we call the force on the bat against the ball the action force, identify the reaction force.
The reaction force is the force by the ball on the bat.
What is the resultant of a pair of one pound forces at right angles to each other?
The resultant is a force of 1.41 pounds in a direction bisecting the 90-degree angle between the two vectors.
Identify the force that propels a rocket.
The rocket is propelled by the reaction force from the particles accelerated out the rear by an action force from the rocket.
The acceleration of free fall is about 10 m/s2. Why does the seconds unit appear twice?
The second appears once in the denominator of the unit for speed and once for the interval of time.
What is the speed acquired by a freely falling object 5 s after being dropped from a rest position? What is the speed 6 s after?
The speed is 50 m/s after 5 s and 60 m/s after 6 s.
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?
The speed of car B is equal to the initial speed of A.
What relationship did Galileo discover about a ball's acceleration and the steepness of an incline? What acceleration occurs when the plane is vertical?
The steeper the incline, the greater the acceleration. On a vertical incline, the ball is in free fall.
Consider Nellie hanging at rest in Figure 2.11. If the ropes were vertical, with no angle involved, what would be the tension in each rope?
The tension in each rope would be half of the gravity force.
How does the magnitude of the vertical component of velocity for a ball tossed at an upward angle change as the ball travels upward? How about the horizontal component of velocity when air resistance is negligible?
The vertical component decreases in magnitude until it reaches the maximum height and then increases; the horizontal component is constant.
If the equally massive cars of the preceding question stick together after colliding inelastically, how does their speed after the collision compare with the initial speed of car A?
Their speed is half the initial speed of car A.
What is the source of energy in sunshine?
Thermonuclear fusion energy
What concept was not understood in the 16th century when people couldn't conceive of a moving Earth?
They did not understand inertia.
How many forces are required for an interaction?
Two forces, an action and a reaction, are needed for an interaction.
Some alphabet letters are floating in a bowl of soup. You want to move a letter that is far away from you closer to you. How could you rotate the bowl to do that? Why?
Unfortunately, neither rotating the bowl clockwise nor rotating it counterclockwise will work. They have inertia−the tendency of an object at rest to stay at rest.
What is the main difference between speed and velocity?
Velocity includes a direction, but speed does not.
A Mack truck and a Volkswagen traveling at the same speed have a head-on collision. The vehicle that undergoes the greatest change in velocity will be the
Volkswagen.
Part complete Calculate the weight in newtons of a 1700-kg elephant. Weight = mg
W = 1.7×10^4 N
Lucy Lightfoot stands with one foot on one bathroom scale and her other foot on a second bathroom scale. Each scale reads 320 N. What is Lucy's weight?
W = 640 N
Part complete In the string-pull illustration in Figure 4.8, a gradual pull of the lower string results in the top string breaking. Does this occur because of the ball's weight or its mass?
Weight
Which varies with location, mass or weight?
Weight varies with location, but mass does not.
What is the condition for an object experiencing free fall?
When gravity is the only force acting on an object, it is in free fall.
Acceleration is generally defined as the time rate of change of velocity. When can it be defined as the time rate of change of speed?
When moving in a straight line, the time rate of change of speed is acceleration.
When is the potential energy of something significant?
When the potential energy changes
Stand next to a wall that travels at 30 km/s relative to the Sun. With your feet on the ground, you also travel at the same 30 km/s. Do you maintain this speed when your feet leave the ground? What concept supports your answer?
When you jump, you continue to move at 30 km/s due to your inertia.
As you stand on a floor, does the floor exert an upward force against your feet? How much force does it exert? Why are you not moved upward by this force?
When you stand on the floor, the floor does exert an upward force against your feet. Your weight is exerted to the floor and the floor resists your weight with an equal upwards force. So, both of the forces will be equal. You are not moved upward by the force because there is no net force acting which allows you to stand still.
A force sets an object in motion. When the force is multiplied by the time of its application, we call the quantity impulse, and an impulse changes the momentum of that object. What do we call the quantity force multiplied by distance?
Work
Is it correct to say that, if no net impulse is exerted on a system, then no change in the momentum of the system will occur?
Yes, always.
If a car moves with a constant velocity, does it also move with a constant speed?
Yes, because constant velocity requires constant speed in the same direction.
A bowling ball at rest is in equilibrium. Is the ball in equilibrium when it moves at constant speed in a straight-line path?
Yes, the bowling ball is in equilibrium because ΣF = 0.
If the system of is only the orange, is there a net force on the system when the apple pulls?
Yes, there is the action of the apple on the orange.
To produce a net force on a system, must there be an externally applied net force?
Yes, there must be an external net force on the system.
Earth pulls down on you with a gravitational force that you call your weight. Do you pull up on Earth with the same amount of force?
Yes, you pull up on Earth with the same force.
As you read this in your chair, how fast are you moving relative to the chair? Relative to the Sun?
You are not moving relative to the chair, but you are moving over 100,000 km/h relative to the Sun.
When you push against a wall with your fingers, they bend. Identify the force or forces involved.
You exert an action force and the wall exerts an equal and opposite reaction force.
Once the crate is sliding, how hard do you push to keep it moving at constant velocity?
You push with a force equal to and opposite the dynamic friction force.
When you stand at rest on a bathroom scale, how does your weight compare with the support force from the scale?
Your weight is equal in magnitude and opposite in direction to the support force from the scale.
How much work is done on a satellite in a circular orbit about Earth?
Zero
Calculate the acceleration of a 290000-kg jumbo jet just before takeoff when the thrust on the aircraft is 170000 N. Acceleration: a=Fnet/m
a = 0.59 m/s^2
If your mass is 90 kg , find your acceleration.
a = 0.51 m/s^2
Which has greater kinetic energy?
a car of half the mass traveling at 60 km/hr
Select the correct equations that show that the acceleration of a hamster is 5 m/s2 when it increases its velocity from rest to 10 m/s in 2 s.
a=Δv/t=(10m/s)/(2s)=5m/s2
A package falls off a truck that is moving at 30 m/s. Neglecting air resistance, the horizontal speed of the package just before it hits the ground is
about 30 m/s.
An archer shoots an arrow. Consider the action force to be the bowstring against the arrow. The reaction to this force is the
arrow's push against the bowstring.
Nellie tosses a ball upward at an angle. Neglecting air resistance, the vertical component of the initial velocity
decreases with time to reach the top.
To impart the greatest momentum to an object, you must
exert the greatest force over the longest time.
When you drop a rubber ball on the floor it bounces back. The force exerted on the ball to produce bouncing is by the
floor.
A bicycle that travels twice as fast as another when braking to a stop will skid
four times as far.
The work you do when pushing a shopping cart twice as far while applying twice the force is
four times as much.
A vehicle undergoes acceleration when it
gains speed, loses speed, and changes its direction
An impulse can be increased by
increasing the force or increasing the time interval.
For every action force, there must be a reaction force that
is equal in magnitude.
What is the unit of work?
joule
Padded dashboards in cars are safer in an accident than non-padded ones because passengers hitting the dashboard encounter
lengthened time of contact.
A force of gravity pulls downward on a book on a table. What force prevents the book from accelerating downward?
normal force
A pair of action-reaction forces always
occur simultaneously.
A hockey puck sliding across the ice finally comes to rest because
of friction.
Momentum = mv What is the momentum of an 7.2-kg bowling ball rolling at 2.2 m/s ?
p = 16 kg⋅m/s
Impulse = Ft What impulse occurs when an average force of 6.0 N is exerted on a cart for 2.8 s ?
p = 17 kg⋅m/s
Nellie tosses a ball upward at an angle. Neglecting air resistance, the horizontal component of the initial velocity
remains constant.
When a big fish swims into an oncoming smaller fish and swallows it, the momentum of the two-fish system _______.
remains the same.
Select the correct equations that show that a freely falling rock drops a distance of 80 m when it falls from rest for 4 s.
s=g⋅t2/2=(10m/s2)⋅(4s)2/2=80m
A bicycle that travels four as fast as another when braking to a stop will skid
sixteen times as far.
When a cannonball is fired, the momentum of the system (cannon + cannonball) is conserved if
the momentum of the cannon is equal to the magnitude of the momentum of the cannon ball and points in the opposite direction.
As the sloped surface supporting a shoe becomes steeper
the normal force becomes less. friction needed to keep it at rest increases. the shoe's weight mg remains unchanged.
A karate expert executes a swift blow and breaks a cement block with her bare hand. The magnitude of the force on her hand is
the same as the force applied to the block.
A car traveling at 100 km/h strikes an unfortunate bug and splatters it. The force of impact is
the same for both.
Both a 50-kg sack is lifted 2 meters from the ground and a 25-kg sack is lifted 4 meters in the same time. The power expended in raising the 50-kg sack is
the same.
A 1000-kg car and a 2000-kg car are hoisted to the same height. Raising the more massive car requires
twice as much work.
The work you do when pushing a shopping cart a given distance while applying twice as much force is
twice as much.
The work you do when pushing a shopping cart twice as far while applying the same force is
twice as much.
You cannot exert a force on a wall
unless the wall simultaneously exerts the same amount of force on you.
A 6.0-kg fish swimming 1.4 m/s swallows an absentminded 1.0-kg fish swimming toward it at a speed that brings both fish to a halt immediately after lunch. Find the speed of the approaching smaller fish before lunch.
v = 8.4 m/s
Emily holds a banana of mass m over the edge of a bridge of height h. She drops the banana and it falls to the river below. Use conservation of energy to find the speed of the banana just before hitting the water.
v = √2gh
Select the correct equations that show that the average speed of a rabbit that runs a distance of 39 m in a time of 3 s is 13 m/s.
v=s/t=(39m)/(3s)=13m/s
When two vehicles collide, momentum is conserved _______.
whether the collision is elastic or inelastic.
While you are standing in the aisle of a bus, the driver suddenly makes a left turn. You lurch to the right due to
your tendency to keep moving forward.
