Deck 5: Momentum and Energy

Question 1

Recoil is noticeable if we throw a heavy ball while standing on roller skates. If instead we go through the motions of throwing the ball but hold onto it, our net recoil will be

A) the same as before.
B) zero.
C) small, but noticeable.

Answer 1

zero.

Question 2

A diver who weighs 500 N steps off a diving board that is 10 m above the water. The diver hits the water with kinetic energy of

A) 5000 J.
B) 500 J.
C) 10 J.
D) more than 5000 J.
E) 510 J.

Answer 2

5000 J.

Question 3

A car moves 4 times as fast as another identical car. Compared to the slower car, the faster car has

A) 8 times the KE.
B) 16 times the KE.
C) 12 times the KE.
D) 4 times the KE.

Answer 3

16 times the KE.

Question 4

A flower pot of mass m falls from rest to the ground below, a distance h. Which statement is correct?

A) The speed of the pot when it hits the ground depends on m.
B) The KE of the pot when it hits the ground does not depend on m.
C) The KE of the pot when it hits the ground is proportional to h.
D) The speed of the pot when it hits the ground is proportional to h.
E) None of these are correct.

Question 5

A bullet is fired from a gun. The speed of the bullet will be about the same as the speed of the recoiling gun

A) because momentum is conserved.
B) if the mass of the bullet equals the mass of the gun.
C) because velocity is conserved.
D) because both velocity and momentum are conserved.
E) none of these

Question 6

One end of a long, uniform log is raised to shoulder level. Another identical log is raised at its center to the same level. Raising the second log requires about

A) the same amount of work.
B) more than twice as much work.
C) twice as much work.

Question 7

When you are in the way of a fast-moving object and can't get out of its way, you will suffer a smaller force of impact if you decrease its momentum over a

A) long time.
B) short time.
C) same way either way

Question 8

Two identical 5000-kg bulldozers roll toward each other on a level road without friction (one at 1 m/s, the other at 2 m/s) Just before they collide, one has a kinetic energy of 2500 J and the other
10,000 J. t this instant their total kinetic energy is

A) 7500 J.
B) 10,000 J.
C) 12,500 J.
D) 1250 J.
E) 2500 J.

Question 9

An object that has kinetic energy must be

A) falling.
B) at an elevated position.
C) moving.
D) at rest.
E) none of these

Question 10

A pile driver hits the top of a telephone pole driving it partway into the ground. The distance that the pole will sink into the ground depends on

A) the original potential energy of the pile driver.weight.
B) the kinetic energy of the pile driver weight when it first contacted the pole.
C) the original height of the pile driver weight.
D) any of the above choices

Question 11

A fan attached to an ice sailcraft stalled on a windless day blows air into the sail that bounces backward upon impact. The boat can

A) then move, but in the opposite direction of the wind impact force.
B) then move in the direction of the wind impact force.
C) not move by this wind impact.

Question 12

A karate expert executes a swift blow and breaks a cement block with her bare hand. The magnitude of the force experienced by her hand is

A) zero.
B) identical to the force applied to the block.
C) less than the force applied to the cement block.
D) more than the force applied to the block.
E) impossible to predict without additional information.

Question 13

A light aluminum ball and a heavy lead ball of the same size are allowed to roll down an incline. When they are halfway down the incline, they will have identical

A) momentum.
B) kinetic energies.
C) inertias.
D) potential energies.
E) none of the above choices

Question 14

A moving object has

A) speed.
B) energy.
C) momentum.
D) velocity.
E) all of these

Question 15

A bullet has more kinetic energy than the recoiling rifle from which it is fired is because the force on the bullet acts over a

A) longer time.
B) longer distance.
C) longer time and a greater distance.

Question 16

A car moving at 50 km/hr skids 20 m with locked brakes. How far will the car skid with locked brakes if it were traveling at 150 km/hr?

A) 20 m
B) 120 m
C) 60 m
D) 90 m
E) 180 m

Question 17

A 5-kg shark swimming at a speed of 1 m/s swallows an absent-minded 1-kg fish swimming toward it at 4 m/s. The speed of the shark after this meal is

A) 2/3 m/s.
B) 1/5 m/s.
C) 1/2 m/s.
D) 3/2 m/s.
E) 1/6 m/s.

Question 18

A 4 kg ball has a momentum of 12 kg m/s. What is the ball's speed?

A) 3 m/s
B) 12 m/s
C) 4 m/s
D) 48 m/s
E) none of these

Question 19

If a monkey floating in outer space throws his hat away, the hat and the monkey will both

A) move away from each other, but at different speeds.
B) move a short distance and then go faster.
C) move a short distance and then slow down.
D) move away from each other at the same speed.
E) come to a stop after a few minutes.

Question 20

Suppose a miracle car has a 100% efficient engine and burns fuel that has a 40-megajoules-per-liter energy content. If the air drag and overall frictional forces on this car
Traveling at highway speeds total 1000 N, what is the overall limit in distance per liter it could be driven on the highway?

A) more than 50 km
B) 30 km
C) 40 km
D) 50 km
E) not enough information

Question 21

In order to catch a ball, a baseball player extends the hand forward before impact with the ball and then lets it ride backward in the direction of the ball's motion .. Doing this reduces the force of impact on the player's hand principally because the

A) relative velocity is less.
B) time of impact is decreased.
C) time of impact is increased.
D) force of impact is reduced.
E) none of these

Question 22

An object at rest may also have

A) speed.
B) kinetic energy.
C) velocity.
D) momentum.
E) potential energy.

Question 23

Do 100 J of work in 50 s and your power output is

A) 2 W.
B) 5,000 W.
C) 50 W.
D) 1/2 W
E) 4 W.

Question 24

A 2 kg mass has 40 J of potential energy with respect to the ground. Approximately how high is it above the ground?

A) 1 m
B) 2 m
C) 3 m
D) 4 m
E) none of these

Question 25

Two 5000-kg passenger cars roll without friction (one at 1 m/s, the other at 2 m/s) toward one another on a level track. They collide, couple, and roll away together with a combined momentum of

A) zero.
B) 5000 kg m/s.
C) 15,000 kg m/s.
D) 10,000 kg m/s.

Question 26

If an object has kinetic energy, then it also must have

A) force.
B) acceleration.
C) impulse.
D) momentum.
E) none of these

Question 27

If you find that twice as much work is needed to perform a task but it takes twice as much time, the amount of power required is

A) sixteen times as much.
B) four times as much.
C) twice as much.
D) unchanged.

Question 28

An astronaut, floating in space, throws a ball as massive as herself toward her nearby spaceship. If the ball bounces back toward her without losing speed, her best choice at that time is to

A) try to catch the ball and then throw it away from the spaceship.
B) forget about catching the ball and wait a few minutes to be rescued.
C) try to catch the ball and wait a few minutes to be rescued.
D) hope that the spaceship pilot is able to rescue her somehow.

Question 29

If a power plant is 30% efficient, and the transmission system that delivers power to consumers is 60% efficient, then the overall efficiency is

A) 60%.
B) 90%.
C) 18%.
D) 30%.
E) none of these

Question 30

A car has a head-on collision with another car that was approaching with the same magnitude of momentum. A third identical car driving with the same speed as the first car runs into an
Enormously massive wall. Which of the four objects will experience the greatest impulse?

A) the second car
B) the approaching car
C) the third car
D) the wall
E) All will receive the same impulse.

Question 31

A 5-kg fish swimming at a speed of 1 m/s swallows an absent-minded 1-kg fish at rest. The speed of the larger fish after this lunch is

A) 1/2 m/s.
B) 1 m/s.
C) 2/5 m/s.
D) 5/6 m/s.
E) 6/5 m/s.

Question 32

A rifle of mass 2 kg is suspended by strings. The rifle fires a bullet of mass 0.01 kg at a speed of 200 m/s. The recoil velocity of the rifle is about

A) 0.01 m/s.
B) 1 m/s.
C) 0.001 m/s.
D) 0.1 m/s.
E) none of these

Question 33

An object may have potential energy because of its

A) momentum.
B) location.
C) acceleration.
D) speed.
E) none of these

Question 34

Two identical objects in outer space have a head-on collision and stick together. If, before the collision, one had been moving at 2 m/s and the other at 1 m/s, their combined speed after the collision would be

A) 0.33 m/s.
B) 1.0 m/s.
C) 0.67 m/s.
D) 0.5 m/s.
E) none of these

Question 35

When a car is braked to a stop, its kinetic energy is transformed to

A) energy of rest.
B) heat.
C) energy of motion.
D) potential energy.
E) stopping energy.

Question 36

After rolling halfway down an incline a marble's kinetic energy is

A) greater than its potential energy.
B) the same as its potential energy.
C) less than its potential energy.
D) impossible to determine.

Question 37

Which requires the most amount of work by the brakes of a car?

A) slowing down from 100 km/h to 70 km/h
B) slowing down from 70 km/h to a stop
C) equal amounts for either

Question 38

A piece of putty moving with 1 unit of momentum strikes and sticks to a heavy bowling ball that is initially at rest. After the putty sticks to the ball, both move with a combined momentum of

A) more than 1 unit.
B) less than 1 unit.
C) 1 unit.
D) not enough information

Question 39

A golf ball is thrown at and bounces backward from a massive bowling ball that is initially at rest. After the collision, compared to the golf ball, the bowling ball has

A) more momentum, but less kinetic energy.
B) less momentum and less kinetic energy.
C) more kinetic energy, but less momentum.
D) more momentum and more kinetic energy.
E) Not enough information is given to say.

Question 40

A hydraulic press, like an inclined plane, is capable of increasing energy.

A) always false
B) sometimes false
C) sometimes true
D) always true

Question 41

How many Joules of energy are in one kilowatt-hour?

A) 60,000
B) 60
C) 1
D) 3.6 million
E) none of these

Question 42

A large metal ball is shot from a cannon with a short barrel. If the same ball were to be shot from cannon with a longer barrel, its muzzle velocity would be

A) more.
B) less.
C) the same.
D) impossible to determine without additional information.

Question 43

On a sunny day about 500 watts of solar power are received by each of the four solar cells on the roof of a solar-powered automobile.. If the solar cells were 100 % efficient, they would deliver

A) 270 hp.
B) 27 hp.
C) 0.27 hp.
D) 2.7 hp.

Question 44

The power required to exert 1 N force, over a distance of 1 m in 1 second is

A) 2 W.
B) 3 W.
C) 1 W.
D) 1/3 W.
E) none of these.

Question 45

If an object is raised twice as high, its potential energy will be

A) twice as much.
B) half as much
C) four times as much.
D) impossible to determine unless the time is given.

Question 46

A 1-kg chunk of putty moving at 1 m/s collides with and sticks to a 5-kg bowling ball initially at rest. The bowling ball and putty then move with a momentum of

A) 1 kg m/s.
B) 5 kg m/s.
C) 0 kg m/s.
D) 2 kg m/s.
E) more than 5 kg m/s.

Question 47

Compared to the recoiling rifle, the bullet fired has

A) a greater momentum.
B) a smaller speed.
C) a greater kinetic energy.
D) all of the above

Question 48

When you jump from an elevated position you usually bend your knees upon reaching the ground. By doing this, you make the time of the impact about 10 times as great as for a stiff-legged landing. In this way the average force your body experiences is

A) about 1/10 as great.
B) about 10 times as great.
C) more than 1/10 as great.
D) less than 1/10 as great.

Question 49

According to the impulse-momentum equation Ft = change in (mv), a person will suffer less injury falling on a wooden floor which "gives" than on a more rigid cement floor. The "F" in the above equation stands for the force exerted on the

A) person.
B) floor.
C) either the force on the person or the force on the floor
D) the sum of the force on the person and the force on the floor

Question 50

A ball rolling down an incline has its maximum kinetic energy at

A) the top.
B) three-quarters of the way down.
C) halfway down.
D) the bottom.

Question 51

You're driving down the highway and a bug spatters into your windshield. Which undergoes the greater change in momentum during the time of contact?

A) the bug
B) your car
C) both the same

Question 52

A ball is projected into the air with 100 J of kinetic energy which is transformed to gravitational potential energy at the top of its trajectory. When it returns to its original level after encountering air resistance, its kinetic energy is

A) more than 100 J.
B) 100 J.
C) less than 100 J.
D) not enough information given

Question 53

A bow is drawn so that it has 40 J of potential energy. When fired, the arrow will ideally have a kinetic energy that is

A) 40 J.
B) more than 40 J.
C) less than 40 J.
D) impossible to predict without additional information

Question 54

A 2500-N pile-driver ram falls 10 m and drives a post 0.1 m into the ground. The average impact force on the ram is

A) 250,000 N.
B) 2,500,000 N.
C) 25,000 N.
D) 2,500 N.

Question 55

A ball rolling down an incline has its minimum speed

A) near the top of the incline.
B) at the end the incline.
C) half way down the incline.
D) impossible to predict without knowing the ball's mass
E) impossible to predict without knowing the size of the ball

Question 56

Two billiard balls having the same mass and speed roll toward each other. What is their combined momentum after they meet ?

A) 0
B) twice the sum of their original momentums
C) half the sum of their original momentums.
D) impossible to determine without additional information

Question 57

A block of ice sliding down an incline has its maximum speed at

A) the bottom.
B) halfway down.
C) the top.
D) difficult to predict without knowing the slope of the incline
E) difficult to predict without knowing the coefficient of friction

Question 58

Two pool balls, each moving at 2 m/s, roll toward each other and collide. Suppose after bouncing apart, each moves at 4 m/s. This collision violates conservation of

A) momentum.
B) energy.
C) both momentum and energy.
D) none of the above choices

Question 59

A car's engine is 20% efficient. When cruising, the car encounters an average retarding force of 1000 N. If the energy content of gasoline is 40 megajoules per liter, how many kilometers per liter does
The car get?

A) 12
B) 8
C) 10
D) 14
E) none of these

Question 60

A motorcycle with a mass of 100 kilograms, slowly rolls over the edge of a cliff and falls for three seconds before it reaches the bottom of a gully. Its momentum ( in units of kilogram meters per second) just before it hit bottom and became burned rubber and scrap metal was

A) 1,000.
B) 4,000.
C) 3,000.
D) 9,000.
E) 2,000.

Question 61

A 2-kg mass is held 4 m above the ground. What is the approximate potential energy of the mass with respect to the ground?

A) 6 J
B) 8 J
C) 80 J
D) 32 J
E) none of these

Question 62

If a ping pong ball and a golf ball are both moving in the same direction with the same amount of kinetic energy, the speed of the ping pong ball must be

A) more than the golf ball.
B) the same as the golf ball.
C) less than the golf ball.
D) impossible to predict without additional information

Question 63

A car that travels twice as fast as another when braking to a stop will skid

A) twice as far.
B) four times as far.
C) depends on the mass of the cars

Question 64

A 1000-kg car moving at 10 m/s brakes to a stop in 5 s. The average braking force is

A) 2000 N.
B) 1000 N.
C) 5000 N.
D) 4000 N.
E) 3000 N.

Question 65

If several balls are thrown straight up with varying initial velocities, the quantity that will have the same value for each trial is the ball's

A) initial momentum.
B) acceleration.
C) time of travel.
D) maximum height.
E) None of the above choices are correct.

Question 66

A 1000-kg car and a 2000-kg car are hoisted the same distance. Raising the more massive car requires

A) twice as much work.
B) as much work.
C) less work.
D) four times as much work.
E) more than four times as much work.

Question 67

Consider massive gliders that slide friction-free along a horizontal air track. Glider A has a mass of 1 kg, a speed of 1 m/s, and collides with Glider B that has a mass of 5 kg and is at rest. If they stick
Upon collision, their speed after collision will be

A) 1 m/s.
B) 1/4 m/s.
C) 1/5 m/s.
D) 1/6 m/s.
E) none of these.

Question 68

A heavy truck and a small car rolling down a hill at the same speed are forced to stop in the same amount of time. Compared to the force that stops the car, the force needed to stop the truck is

A) greater.
B) the same.
C) smaller.

Question 69

Which has greater kinetic energy, a car traveling at 30 km/hr or a car of half the mass traveling at 60 km/hr?

A) the 30 km/hr car
B) the 60 km/hr car
C) Both have the same kinetic energy.
D) More information is needed about the distance traveled.

Question 70

The change in momentum, in kg m/s, that occurs when a 1.0 kg ball travelling at 4.0 m/s strikes a wall and bounces back at 2.0 m/s is

A) 4.
B) 8.
C) 2.
D) 6.

Question 71

A machine puts out 100 Watts of power for every 1000 Watts put into it. The efficiency of the machine is

A) 10%.
B) 90%.
C) 110%.
D) 50%.
E) none of these

Question 72

A 1-kg chunk of putty moving at 1 m/s collides with and sticks to a 5-kg bowling ball that is initially at rest on a frictionless surface. The speed of the putty thereafter is

A) 1/5 m/s.
B) 1/6 m/s.
C) 1/4 m/s.
D) impossible to solve with the information given.

Question 73

Whereas impulse involves the time that a force acts, work involves the

A) acceleration that a force produces.
B) time and distance that a force acts.
C) distance that a force acts.

Question 74

The force on an apple hitting the ground depends upon

A) whether or not the apple bounces.
B) the speed of the apple just before it hits.
C) the time of impact with the ground.
D) all of these

Question 75

A TV set is pushed a distance of 2 m with a force of 20 N. How much work is done on the set?

A) 40 J
B) 20 J
C) 10 J
D) 800 J
E) 2 J

Question 76

A 1-kg glider and a 2-kg glider both slide toward each other at 1 m/s on an air track. They collide and stick. The combined mass moves at

A) 1/2 m/s.
B) 1/6 m/s.
C) 1/3 m/s.
D) 0 m/s.
E) 1.5 m/s.

Question 77

Two objects have the same size and shape, but one is much heavier than the other. When they are dropped simultaneously from a tower, they reach the ground at the same time, but the heavier one has a greater

A) momentum.
B) acceleration.
C) speed.
D) all of these
E) none of these

Question 78

A rifle recoils while firing a bullet. The speed of the rifle's recoil is small because the

A) force against the rifle is smaller than against the bullet.
B) rifle has much more mass than the bullet.
C) momentum of the rifle is smaller.
D) momentum is mainly concentrated in the bullet.

Question 79

If the speed of a moving object doubles, which of the following also doubles?

A) kinetic energy
B) acceleration
C) momentum
D) all of the above

Question 80

A clerk can lift containers a vertical distance of 1 meter or can roll them up a 2 meter-long ramp to the same elevation. With the ramp, the applied force required is about

A) the same.
B) twice as much.
C) four times as much.
D) half as much.