Physics Exam 2
To understand the distinction between mass and weight and to be able to calculate the weight of an object from its mass and Newton's law of gravitation. The concepts of mass and weight are often confused. In fact, in everyday conversations, the word "weight" often replaces "mass," as in "My weight is seventy-five kilograms" or "I need to lose some weight." Of course, mass and weight are related; however, they are also very different. Mass, as you recall, is a measure of an object's inertia (ability to resist acceleration). Newton's 2nd law demonstrates the relationship among an object's mass, its acceleration, and the net force acting on it: Fnet=ma. Mass is an intrinsic property of an object and is independent of the object's location. Weight, in contrast, is defined as the force due to gravity acting on the object. That force depends on the strength of the gravitational field of the planet: w=mg, where w is the weight of an object, m is the mass of that object, and g is the local acceleration due to gravity (in other words, the strength of the gravitational field at the location of the object). Weight, unlike mass, is not an intrinsic property of the object; it is determined by both th
0.34g and 120 kg
What will be the kinetic energy of a pile driver ram starting from rest that undergoes a 10-kJ decrease in potential energy?
10 kJ
A 3.6 kg chihuahua charges at a speed of 3.3m/s. What is the magnitude of the average force needed to bring the chihuahua to a stop in 0.50s?
24N
A hungry fish is about to have lunch at the speeds shown below. Assume the hungry fish has a mass 5 times that of the small fish. Immediately after lunch, rank the speed of the formerly hungry fish from each case from greatest to least.
Greatest C, A, B Least
Rank KE from greatest to least at each point.
Greatest D, B, C, E, A Least
Rank speed from greatest to least at each point.
Greatest D, B, C, E, A Least
Imagine that you replace the block in the video with a happy or sad ball identical to the one used as a pendulum, so that the sad ball strikes a sad ball and the happy ball strikes a happy ball. The target balls are free to move, and all the balls have the same mass. In the collision between the sad balls, how much of the balls' kinetic energy is dissipated?
Half of it
How does Dr. Hewitt break the piece of wood?
He causes a change in momentum of his hand over a short period of time.
Find the "missing energy".
Q= 770 J
Click "Reset." Now, predict what will happen if you increase the mass of the green truck so that it is greater than the mass of the red truck.
The trucks will stick together after the collision and move to the right.
Click "Reset." Now, predict what will happen if you change the velocity of the red truck so that it has a magnitude smaller than that of the green truck but is negative.
The trucks will stick together after the collision and move to the right. Submit
Energy cannot be _______.
destroyed
During a certain time interval, the net work done on an object is zero joules. We can be certain that ____.
the object's final speed was the same as its initial speed
To understand the distinction between mass and weight and to be able to calculate the weight of an object from its mass and Newton's law of gravitation. The concepts of mass and weight are often confused. In fact, in everyday conversations, the word "weight" often replaces "mass," as in "My weight is seventy-five kilograms" or "I need to lose some weight." Of course, mass and weight are related; however, they are also very different. Mass, as you recall, is a measure of an object's inertia (ability to resist acceleration). Newton's 2nd law demonstrates the relationship among an object's mass, its acceleration, and the net force acting on it: Fnet=ma. Mass is an intrinsic property of an object and is independent of the object's location. Weight, in contrast, is defined as the force due to gravity acting on the object. That force depends on the strength of the gravitational field of the planet: w=mg, where w is the weight of an object, m is the mass of that object, and g is the local acceleration due to gravity (in other words, the strength of the gravitational field at the location of the object). Weight, unlike mass, is not an intrinsic property of the object; it is determined by both th
12.0 lbs and 1600 kN and 899 MN
If you push a crate horizontally with 100 N across a 10-m factory floor and friction between the crate and the floor is a steady 70 N, how much kinetic energy is gained by the crate?
300J
A 1700kg rhino charges at a speed of 50.0 km/h. What is the magnitude of the average force needed to bring the rhino to a stop in 0.50s?
470000 or 4.7×10<4 N
If the acceleration due to gravity on the earth is 9.8 m/s2, what is the acceleration due to gravity on Rams?
5.7 m/s2
When the useful energy output of a simple machine is 100 J, and the total energy input is 200 J, the efficiency is _______.
50 percent
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%
Shown below is a graph of a force applied to a small object as a function of time. If the object has a mass of 5.0kg and is at rest at t=0s, how fast is the object moving at t=4.0s?
7.2 m/s
Why does the bowling ball behave the way it does the first time Dr. Hewitt lifts the bowling ball near his teeth and lets go?
All of the initial energy of the ball was converted completely back to potential energy when the ball returned.
In the opening scenes of the prelecture video, we outlined some of the key properties of momentum. Which of the following statements are consistent with these properties?
An object's momentum is equal to the product of its mass and its velocity. Momentum is a vector quantity.
When Dr. Hewitt releases the two projectiles, which one hits the ground first?
Both balls hit the ground at the same time.
F=G m1m2/r<2 Calculate the force of gravity on a 1-kg mass if it were 1.3×107m above Earth's surface (that is, if it were three Earth radii from Earth's center).
F = 1.1 N
Find the change in the gravitational force between two planets if the masses of both planets are doubled but the distance between them stays the same.
Fnew/F= 4
Why do the two objects hit the table at the relative times that they do?
Gravity pulls the same amount on each ball, and they each drop the same distance.
Rank the microtidal forces on your own body, from greatest to least, produced by the following:
Greastest Earth, Jupiter, Pluto Least
Rank PE from greatest to least at each point.
Greatest A, E, C, B, D Least
How is Dr. Hewitt able to break a piece of wood in his demonstration?
He moves his hand very quickly.
Impulse = change in momentum: Ft=Δmv How much impulse stops a 45-kg carton sliding at 5.2 m/s when it meets a rough surface
I= 230 N⋅s
What would Dr. Hewitt need to have done to exert an even greater force than he did in his karate demonstration?
Increase the change in momentum, and decrease the time duration.
Predict how the vertical component of the velocity will change with time after the projectile is fired.
It first decreases to zero and then increases in the opposite direction.
Predict how the horizontal component of the velocity will change with time after the projectile is fired.
It stays constant.
Suppose our experimenter repeats his experiment on a planet more massive than Earth, where the acceleration due to gravity is g=30 m/s2�=30 m/s2. When he releases the ball from chin height without giving it a push, how will the ball's behavior differ from its behavior on Earth? Ignore friction and air resistance. (Select all that apply.)
It will take less time to return to the point from which it was released.
If the force of friction on the crate is a steady 70 N, find the KE gained by the crate.
K= 770J
Kinetic energy = 1/2 mass × speed<2 : KE = 1/2mv<2 Calculate the kinetic energy of a 106-kg scooter moving at 10 m/s
KE= 5300 J
In which type or kind of collision is momentum conserved: elastic or inelastic?
Momentum is conserved in elastic and inelastic collisions.
Now, consider the collision between two happy balls described in Part A. How much of the balls' kinetic energy is dissipated?
None of it
For an Earth satellite in circular orbit, list all the values that do not change.
Only speed, gravitational force, and distance from Earth
Bumper cars A and B undergo a collision during which the momentum of the combined system is conserved. Which equation(s) correctly states the principle of conservation of momentum?
PA,i+PB,i=PA,f+PB,f
Which planet should Punch travel to if his goal is to weigh in at 118 lb? Refer to the table of planetary masses and radii given to determine your answer.
Pentune
A small toy cart equipped with a spring bumper rolls toward a wall with a speed of v. The cart rebounds from the wall, with the same speed v. The sketch below shows the initial velocity vector vi, final velocity vector vf, and the initial momentum vector pi. Using the initial momentum vector as a basis, draw the change in momentum vector Δp for the cart. You can obtain each vector's length and orientation by clicking on it to select it.
Picture
Part A Part complete Each of the following diagrams shows a spaceship somewhere along the way between Earth and the Moon (not to scale); the midpoint of the distance is marked to make it easier to see how the locations compare. Assume the spaceship has the same mass throughout the trip (that is, it is not burning any fuel). Rank the five positions of the spaceship from left to right based on the strength of the gravitational force that Earth exerts on the spaceship, from strongest to weakest.
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The amount of kinetic energy an object has depends on its mass and its speed. Rank the following sets of oranges and cantaloupes from least kinetic energy to greatest kinetic energy. If two sets have the same amount of kinetic energy, place one on top of the other.
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The following diagrams are the same as those from Part A. Again considering only the two objects shown in each pair, this time rank the strength, from strongest to weakest, of the gravitational force acting on the object on the right.
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The following diagrams are the same as those from Part A. This time, rank the five positions of the spaceship from left to right based on the strength of the gravitational force that the Moon exerts on the spaceship, from strongest to weakest.
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The following diagrams are the same as those from Part A. This time, rank the pairs from left to right based on the size of the acceleration the asteroid on the left would have due to the gravitational force exerted on it by the object on the right, from largest to smallest.
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The following diagrams show five pairs of asteroids, labeled with their relative masses (M) and distances (d) between them. For example, an asteroid with M=2 has twice the mass of one with M=1 and a distance of d=2 is twice as large as a distance of d=1. Rank each pair from left to right based on the strength of the gravitational force attracting the asteroids to each other, from strongest to weakest.
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The following five diagrams show pairs of astronomical objects that are all separated by the same distance d. Assume the asteroids are all identical and relatively small, just a few kilometers across. Considering only the two objects shown in each pair, rank the strength, from strongest to weakest, of the gravitational force acting on the asteroid on the left.
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The planet and its moon gravitationally attract each other. Rank the force of attraction between each pair from greatest to least.
Picture
Object A has a mass m and a speed v, object B has a mass m/2 and a speed 4v, and object C has a mass 3m and a speed v/3. Rank the objects according to the magnitude of their momentum.
Smallest momentum Object C and Object A, Object B Largest momentum
For an Earth satellite in an elliptical orbit, list all the values that change.
Speed, gravitational force, and distance from Earth
The video shows an animated billiards experiment in which a cue ball strikes a glued-in-place eight-ball. Which of the following explains why the momentum of the eight-ball is conserved?
The "glue force" cancels the collision force.
Why does the gravity in the Space Shuttle compare with the gravity on Earth the way it does?
The Space Shuttle and the surface of the Earth are about the same distance from the center of the Earth.
Why do the astronauts in the Space Shuttle float around?
The Space Shuttle is in free fall, so the shuttle and the astronauts inside it are continuously falling toward the Earth. They thus experience apparent weightlessness.
What happens the second time Dr. Hewitt lifts the bowling ball near his teeth and gives it a push?
The ball leaves Dr. Hewitt and returns to him, going past the point where it was released.
What happens the first time Dr. Hewitt lifts the bowling ball near his teeth and lets go?
The ball returns to Dr. Hewitt, stopping almost exactly at the point where it was released.
Which ball (if either) has the greatest speed at the moment of impact?
The ball thrown horizontally
As you found in Part A, your weight will be greater than normal when the elevator is moving upward with increasing speed. For what other motion would your weight also be greater than your normal weight?
The elevator moves downward while slowing in speed.
Why does the bowling ball behave as it does when Dr. Hewitt lifts it and gives it a push?
The extra energy from the push is converted into kinetic energy, which is then converted into more potential energy at the end of the motion than the ball had when it was released.
Why doesn't the force of gravity change the speed of a satellite in circular orbit?
The force is at a right angle to the velocity.
How does the gravity in the Space Shuttle compare with the gravity on Earth's surface?
The gravity in the Space Shuttle is approximately equal to the gravity on the surface of the Earth.
Which statement must be true for the momentum of a system to be conserved?
The net external force on the system is zero.
While goofing off at the ice skating rink, a student takes off her shoes and places each of them on the ice. Her friend, a hockey player, then shoots a hockey puck at each shoe. The first puck immediately comes to rest after it collides with the left shoe. The second puck rebounds after it collides with the right shoe. If each hockey puck has the same incoming speed, which shoe has greater speed after the collision?
The right shoe
Predict what will happen if you reduce the magnitude of the velocity of the green truck to a magnitude smaller than that of the red truck.
The trucks will stick together after the collision and move to the left.
Click "Reset." Now, predict what will happen if you change the velocity of the red truck so that it has a magnitude smaller than that of the green truck but is positive.
The trucks will stick together after the collision and move to the right.
Before you click "Play," predict what will happen if the red and green truck with equal mass and equal magnitude of velocity collide.
The trucks will stick together after the collision and not move.
Predict how the upward force exerted on the feet by the scale will compare to the man's weight if the elevator is moving downward at a constant speed.
The upward force on the feet will be equal to the man's weight.
Predict how the upward force exerted on the feet by the scale will compare to the weight of the man if the elevator is moving upward at a constant speed.
The upward force on the feet will be equal to the man's weight. Submit
Predict how the upward force exerted on the feet by the scale will compare to the man's weight if the elevator is accelerating downward.
The upward force on the feet will be less than the man's weight.
Predict how the upward force exerted on the feet by the scale will compare to the man's weight if the elevator is accelerating upward.
The upward force on the feet will exceed the man's weight.
How much work is done when you push a crate horizontally with 140 N across a 11-m factory floor?
W= 1500 J
Where do you weigh more--at the bottom of Death Valley or atop one of the peaks of the Sierra Nevada? Defend your answer.
You weigh more in Death Valley because you are closer to the center of Earth.
When traveling twice as fast your kinetic energy is increased _______.
by four times
A boxer rides with the punch so as to reduce ___________.
force
When you lift twice the load twice as high, in half the time, the increase in potential energy is _______.
four times
The work that is done when twice the load is lifted twice the distance is _______.
four times as much
If acceleration due to gravity on the earth is g, which formula gives the acceleration due to gravity on Loput?
g 5.6/1.7<2
Suppose you are in an elevator. As the elevator starts upward, its speed will increase. During this time when the elevator is moving upward with increasing speed, your weight will be __________.
greater than your normal weight at rest
Cassy can get more force on the bricks she breaks with a blow of her bare hand when _______.
her hand is made to bounce from the bricks
A slowly moving ship can have a greater momentum than a fast-moving racing car when _______.
its mass times velocity is greater than that of the car
Suppose you are in an elevator that is moving upward. As the elevator nears the floor at which you will get off, its speed slows down. During this time when the elevator is moving upward with decreasing speed, your weight will be __________.
less than your normal weight at rest
The constant G in Newton's equation _______.
makes the units of measurement consistent
After Punch Taut travels to Pentune, what actually happens to his mass and his weight?
mass remains the same; weight decreases
An object is lifted from the surface of a spherical planet to an altitude equal to the radius of the planet. As a result, which of the following changes in the properties of the object take place?
mass remains the same; weight decreases
A motorcycle drives up a steeply inclined ramp. The work done on the motorcycle by the Earth's gravitational force is ____.
negative
Impulse: I=Ft What impulse occurs when an average force of 13 N is exerted on a cart for 2.4 s?
p = 31 N⋅s
Momentum: p=mv What is the momentum of a 9.0-kgkg bowling ball rolling at 2.4 m/sm/s?
p= 22 kg⋅m/s
The quantity that is called impulse can be measured by the _______.
product of force and time
When a big fish swims into an oncoming smaller fish and swallows it, the momentum of the two-fish system _______.
remains the same
Consider Earth and the Moon. As you should now realize, the gravitational force that Earth exerts on the Moon is equal and opposite to that which the Moon exerts on Earth. Therefore, according to Newton's second law of motion __________.
the Moon has a larger acceleration than Earth, because it has a smaller mass
The elevator moves downward while slowing in speed.
the force you exert on the scale
When one does twice the work in twice the time, the power expended is _______.
the same
Two identical cars are driving in opposite directions at the same speed. Their kinetic energies have ____.
the same magnitude and sign
Fossil fuels, hydroelectric power, and wind power ultimately get their energy from _______.
the sun
A 5.5-kg fish swimming 0.60 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 = 3.3 m/s
Emily drops a banana of mass m over the edge of a bridge of height h and it falls to the river below. From the initial PE of the banana converting to KE, find the speed of the banana just before hitting the water.
v =√2gℎ
The gravitational field on the surface of the earth is stronger than that on the surface of the moon. If a rock is transported from the moon to the earth, which properties of the rock change?
weight only
When two vehicles collide, momentum is conserved _______.
whether the collision is elastic or inelastic
