Deck 7: Work and Energy

Question 1

Two objects,one of mass m and the other of mass 2m,are dropped from the top of a building.Assuming there is no air resistance,when they hit the ground

A)both will have the same kinetic energy.
B)the heavier one will have twice the kinetic energy of the lighter one.
C)the heavier one will have four times the kinetic energy of the lighter one.
D)the heavier one will have half the kinetic energy of the lighter one.
E)the heavier one will have one-fourth the kinetic energy of the lighter one.

Answer 1

B

Question 2

Which requires more work,increasing a car's speed from 0 mph to 30 mph or from 50 mph to 60 mph?

A)0 mph to 30 mph
B)50 mph to 60 mph
C)It is the same in both cases.

Answer 2

B

Question 3

When you throw a pebble straight up with initial speed V,it reaches a maximum height H assuming there is no air resistance.At what speed should you throw it up vertically so it will go twice as high?

A)16V
B)8V
C)4V
D)2V
E) V

Answer 3

E

Question 4

Person X pushes twice as hard against a stationary brick wall as person Y.Which one of the following statements is correct?

A)Both do positive work, but person X does four times the work of person Y.
B)Both do positive work, but person X does twice the work of person Y.
C)Both do the same amount of positive work.
D)Both do zero work.
E)Both do positive work, but person X does one-half the work of person Y.

Question 5

Two men,Joel and Jerry,push against a car that has stalled,trying unsuccessfully to get it moving.Jerry stops after 10 min,while Joel is able to push for 5.0 min longer.Compare the work they do on the car.

A)Joel does 75% more work than Jerry.
B)Joel does 50% more work than Jerry.
C)Jerry does 50% more work than Joel.
D)Joel does 25% more work than Jerry.
E)Neither of them does any work.

Question 6

A stone is held at a height h above the ground.A second stone with four times the mass of the first one is held at the same height.The gravitational potential energy of the second stone-Earth system compared to that of the first stone-Earth system is

A)one-fourth as much.
B)one-half as much.
C)twice as much.
D)four times as much.
E)the same.

Question 7

A truck has four times the mass of a car and is moving with twice the speed of the car.If K_t and K_c refer to the kinetic energies of truck and car respectively,it is correct to say that

A)K_t = 16K_c.
B)K_t = 4K_c.
C)K_t = 2K_c.
D)K_t = K_c.
E)K_t = Kc.

Question 8

When you drop a pebble from height H,it reaches the ground with speed V assuming there is no air resistance.From what height should you drop it so it will reach the ground with twice speed?

A) H
B)2H
C)4H
D)8H
E)16H

Question 9

You slam on the brakes of your car in a panic,and skid a certain distance on a straight level road.If you had been traveling twice as fast,what distance would the car have skidded,under the same conditions?

A)It would have skidded 4 times farther.
B)It would have skidded twice as far.
C)It would have skidded 1.4 times farther.
D)It would have skidded one half as far.
E)It is impossible to tell from the information given.

Question 10

If the force exerted on an object is in the negative direction,the work it does on the object must be

A)negative.
B)positive.
C)The work could be either positive or negative, depending on the direction the object moves.

Question 11

A 35-N bucket of water is lifted vertically 3.0 m and then returned to its original position.How much work did the gravitational force exerted by Earth on the object do on the bucket during this process?

A)180 J
B)90 J
C)45 J
D)0 J
E)900 J

Question 12

You throw a baseball straight up.Compare the sign of the work done by the gravitational force exerted by Earth on the object while the ball goes up with the sign of the work done by the same force while it goes down.

A)The work is positive on the way up and positive on the way down.
B)The work is positive on the way up and negative on the way down.
C)The work is negative on the way up and positive on the way down.
D)The work is negative on the way up and on the way down because gravity is always downward.

Question 13

Which one has larger kinetic energy: a 500-kg object moving at 40 m/s or a 1000-kg object moving at 20 m/s?

A)The 500-kg object
B)The 1000-kg object
C)Both have the same kinetic energy.

Question 14

A heavy dart and a light dart are launched horizontally on a frictionless table by identical ideal springs.Both springs were initially compressed by the same amount.Which of the following statements about these darts are correct? (There could be more than one correct choice.)

A)The darts both have the same kinetic energy just as they move free of the spring.
B)The lighter dart leaves the spring moving faster than the heavy dart.
C)The heavy dart had more initial elastic potential energy than the light dart.
D)Both darts move free of the spring with the same speed.
E)Both darts had the same initial elastic potential energy.

Question 15

Three cars (car F,car G,and car H)are moving with the same speed and slam on their brakes.The most massive car is car F,and the least massive is car H.If the tires of all three cars have identical coefficients of kinetic friction with the road surface,which car travels the longest distance to skid to a stop?

A)They all travel the same distance in stopping.
B)Car F
C)Car G
D)Car H

Question 16

A 4.0 kg object is moving with speed 2.0 m/s.A 1.0 kg object is moving with speed 4.0 m/s.The same stopping force is exerted on both objects and both objects are brought to rest.Which object travels the greater distance before stopping?

A)the 4.0 kg object
B)the 1.0 kg object
C)Both objects travel the same distance.
D)It cannot be determined from the information given.

Question 17

Three cars (car L,car M,and car N)are moving with the same speed and slam on their brakes.The most massive car is car L,and the least massive is car N.If the tires of all three cars have identical coefficients of kinetic friction with the road surface,for which car is the amount of work done by friction in stopping it the greatest?

A)The amount of work done by friction is the same for all cars.
B)Car L
C)Car M
D)Car N

Question 18

When you drop a pebble from height H,it reaches the ground with kinetic energy K assuming there is no air resistance.From what height should you drop it so it will reach the ground with twice as much kinetic energy?

A) H
B)2H
C)4H
D)8H
E)16H

Question 19

The graphs shown show the magnitude F of the force exerted by a spring as a function of the distance x the spring has been stretched.For which one of the graphs does the spring obey Hooke's law?

A)Graph a
B)Graph b
C)Graph c
D)Graph d
E)Graph e

Question 20

You and your friend,who has the same mass as you,want to go to the top of the Eiffel Tower.Your friend takes the elevator straight up.You decide to walk up the spiral stairway,taking longer to do so.Compare the gravitational potential energy of the system you-Earth and your friend-Earth,after you both reach the top.

A)It is impossible to tell, since the times you both took are unknown.
B)It is impossible to tell, since the distances you both traveled are unknown.
C)The friend-Earth system's gravitational potential energy is greater than the you-Earth system's gravitational potential energy, because he got to the top faster.
D)Both systems have the same amount of gravitational potential energy at the top.
E)The you-Earth system's gravitational potential energy is greater than the friend-Earth system, because you traveled a greater distance in getting to the top.

Question 21

A lightweight object and a very heavy object are sliding with equal speeds along a level frictionless surface.They both slide up the same frictionless hill with no air resistance.Which object rises to a greater height?

A)The heavy object, because it has greater initial kinetic energy.
B)The light object, because gravity slows it down less.
C)The lightweight object, because the gravitational force exerted on it is less.
D)The heavy object, because it has more mass to carry it up the hill.
E)They both slide to exactly the same height.

Question 22

Joe and Bill throw identical balls vertically upward.Joe throws his ball with an initial speed twice as high as Bill.Assuming there is no air resistance,the maximum height of Joe's ball will be

A)four times that of Bill's ball.
B)two times that of Bill's ball.
C)equal to that of Bill's ball.
D)eight times that of Bill's ball.
E)roughly 1.4 times that of Bill's ball.

Question 23

Two frisky otters slide down frictionless hillsides of the same height but different slopes.The slope of the hill of otter 1 is 30°,while the slope of the hill of otter 2 is 60°.If both start from rest,which otter is moving faster when she reaches the bottom of her hill?

A)Otter 1 is moving faster.
B)Otter 2 is moving faster.
C)The heavier otter is moving faster, no matter which hill she used.
D)Both otters have the same speed at the bottom.
E)The otter that took the shorter time is moving faster.

Question 24

A heavy sled and a light sled,both moving horizontally with the same speed,suddenly slide onto a rough patch of snow and eventually come to a stop.The coefficient of kinetic friction between the sleds and the rough snow is the same for both of them.Which of the following statements about these sleds are correct? (There could be more than one correct choice.)

A)Both sleds will slide the same distance on the rough snow before stopping.
B)The heavy sled will slide farther on the rough snow than the light sled.
C)The light sled will slide farther on the rough snow than the heavy sled.
D)The friction force exerted on the sled by the snow will do more negative work on the heavy sled than on the light sled.
E)The friction force exerted on the sled by the snow will do the same amount of work on both sleds.

Question 25

A force is exerted on a system doing work W in a time T.What will be the power of the process that involves a force that does six times as much work in half as much time?

A)12P
B)6P
C)P
D) P
E) P

Question 26

A heavy stone and a light stone are released from rest in such a way that the amount of gravitational potential energy of the system rock-Earth for each rock is the same just as they are released.Air resistance is negligibly small.Which of the following statements about these stones are correct? (There could be more than one correct choice.)

A)The initial height of the light stone is greater than the initial height of the heavy stone.
B)The stones must have been released from the same height.
C)The stones both have the same speed just as they reach the ground.
D)Just as it reaches the ground, the light stone is traveling faster than the heavy stone.
E)The stones both have the same kinetic energy just as they reach the ground.

Question 27

In an inelastic collision involving an isolated system,the final total momentum is

A)exactly the same as the initial momentum.
B)more than the initial momentum.
C)less than the initial momentum.

Question 28

Two cyclists who weigh the same and have identical bicycles ride up the same mountain,both starting at the same time.Joe rides straight up the mountain,and Bob rides up the longer road that has a lower grade.Joe gets to the top before Bob.Ignoring friction and wind resistance,which one of the following statements is true?

A)The amount of internal energy converted to gravitational potential energy of the system Joe- Earth is equal to the amount of of internal energy converted to gravitational potential energy of the system Bob-Earth, but the average power of the process for Joe is greater than that for Bob.
B)The amount of internal energy converted to gravitational potential energy of the system Joe- Earth is greater than the amount of internal energy converted to gravitational potential energy of the system Bob-Earth, and the average power of the process for Joe is greater than that for Bob.
C)Bob and Joe converted the same amount of internal energy to gravitational potential energy, and the average power of the process for each cyclist was also the same.
D)The average power of the process for Bob and Joe was the same, but Joe converted more of the internal energy into the gravitational potential energy in getting there.

Question 29

Two identical grasshoppers jump with the same initial speed.Grasshopper A goes straight up,but grasshopper B goes up at a 66° angle above the horizontal.Assume no air resistance and choose your system to be grasshopper-Earth.Which of the following statements about these grasshoppers are correct? (There could be more than one correct choice.)

A)At their highest point, both systems have the same amount of gravitational potential energy.
B)At their highest point, both systemshave the same amount of kinetic energy.
C)At their highest point, both systemshave the same amount of mechanical energy.
D)At their highest point, grasshopper B is moving faster than grasshopper A.
E)At their highest point, the system grasshopper A-Earth has more gravitational potential energy than the system grasshopper B-Earth.

Question 30

A heavy dart and a light dart are launched vertically by identical ideal springs.Both springs were initially compressed by the same amount.There is no significant air resistance.Which of the following statements about these darts are correct? (There could be more than one correct choice.)

A)The heavy dart goes higher than the light dart.
B)The light dart goes higher than the heavy dart.
C)Both darts reach the same maximum height.
D)At the maximum height, the systems consisting of each dart and Earth have the same gravitational potential energy.
E)Both darts began moving upward with the same initial speed.

Question 31

A stone can slide down one of four different frictionless ramps,as shown in the figure.For which ramp will the speed of the ball be the greatest at the bottom?

A)Ramp X
B)Ramp Y
C)Ramp Z
D)The speed of the ball will be the same for all ramps.

Question 32

A 1-kg ball is released from a height of 6 m,and a 2-kg ball is released from a height of 3 m.Air resistance is negligible as they fall.Which of the following statements about these balls are correct? (There could be more than one correct choice.)

A)As they reach the ground, the 1-kg ball will have more kinetic energy than the 2-kg ball because it was dropped from a greater height.
B)As they reach the ground, the 1-kg ball will be moving faster than the 2-kg ball.
C)Both balls will reach the ground with the same speed.
D)Both balls will reach the ground with the same kinetic energy.
E)Both balls will take the same time to reach the ground.

Question 33

Swimmers at a water park have a choice of two frictionless water slides,as shown in the figure.Although both slides drop over the same height h,slide 1 is straight while slide 2 is curved,dropping quickly at first and then leveling out.How does the speed v₁ of a swimmer reaching the bottom of slide 1 compare with v₂,the speed of a swimmer reaching the end of slide 2?

A)v₁ > v₂
B)v₁ < v₂
C)v₁ = v₂
D)The heavier swimmer will have a greater speed than the lighter swimmer, no matter which slide he uses.
E)No simple relationship exists between v₁ and v₂.

Question 34

The momentum of an isolated system is conserved

A)only in inelastic collisions.
B)only in elastic collisions.
C)in both elastic and inelastic collisions.

Question 35

A heavy sled and a light sled,both moving horizontally with the same kinetic energy,suddenly slide onto a rough patch of snow and eventually come to a stop.The coefficient of kinetic friction between the sleds and the rough snow is the same for both of them.Which of the following statements about these sleds are correct? (There could be more than one correct choice.)

A)Both sleds will slide the same distance on the rough snow before stopping.
B)The heavy sled will slide farther on the rough snow than the light sled.
C)The light sled will slide farther on the rough snow than the heavy sled.
D)On the rough snow, the change in kinetic energy will be the same for both sleds.
E)The friction force exerted on the sleds by the snow will do the same amount of work on both sleds.

Question 36

A girl throws a stone from a bridge.Consider the following ways she might throw the stone.The speed of the stone as it leaves her hand is the same in each case. Case A: Thrown straight up.
Case B: Thrown straight down.
Case C: Thrown out at an angle of 45° above horizontal.
Case D: Thrown straight out horizontally.
In which case will the speed of the stone be greatest when it hits the water below if there is no significant air resistance?

A)Case A
B)Case B
C)Case C
D)Case D
E)The speed will be the same in all cases.

Question 37

A heavy rock and a light rock are dropped from the same height.The forces exerted on them by air are negligible.Which of the following statements about these rocks are correct? (There could be more than one correct choice.)

A)Both rocks have the same kinetic energy when they reach the ground.
B)Both rocks have the same speed when they reach the ground.
C)The heavier rock reaches the ground before the lighter rock.
D)Just as they were released, the two systems consisting of each rock and Earth had the same amount of gravitational potential energy.
E)When they reach the ground, the heavier rock has more kinetic energy than the lighter rock.

Question 38

A person stands on the edge of a cliff.She throws three identical rocks with the same speed.Rock X is thrown vertically upward,rock Y is thrown horizontally,and rock Z is thrown vertically downward.If the ground at the base of the cliff is level,which rock hits the ground with the greatest speed if there is no air resistance?

A)Rock X
B)Rock Y
C)Rock Z
D)They all hit the ground with the same speed.

Question 39

If the units of your answer are kg ∙ m²/s³,which of the following types of quantities could your answer be? (There could be more than one correct choice.)

A)kinetic energy
B)potential energy
C)force
D)power
E)work

Question 40

If a stone is dropped so that the initial gravitational potential energy of the system stone-Earth is 100 J but it reaches the ground with a kinetic energy of only 75 J,this is a violation of the principle of conservation of energy.

Question 41

In the figure,determine the character of the collision.The masses of the blocks,and the velocities before and after,are shown.The collision is

A)perfectly elastic.
B)partially inelastic.
C)completely inelastic.
D)characterized by an increase in kinetic energy.
E)not possible because momentum is not conserved.

Question 42

Two objects of different mass have equal,non-zero kinetic energies.Which object has the greater magnitude momentum?

A)the heavier object
B)the lighter object
C)They both have the same magnitude momentum.

Question 43

In the figure,determine the character of the collision.The masses of the blocks,and the velocities before and after,are shown.The collision is

A)perfectly elastic.
B)partially inelastic.
C)completely inelastic.
D)characterized by an increase in kinetic energy.
E)not possible because momentum is not conserved.

Question 44

A child does 350 J of work while pulling a box from the ground up to his tree house at a steady speed with a light rope.The tree house is above the ground.What is the mass of the box?

A)8.9 kg
B)5.3 kg
C)6.7 kg
D)8.0 kg

Question 45

In a game of pool,the white cue ball hits the #5 ball and stops,while the #5 ball moves away with the same velocity as the cue ball had originally.Both balls have the same mass.This type of collision is

A)somewhat inelastic.
B)elastic.
C)completely inelastic.

Question 46

You carry a 7.0-kg bag of groceries above the ground at constant speed across a room.How much work do you do on the bag in the process?

A)0.00 J
B)82 J
C)185 J
D)157 J

Question 47

If you want to double the kinetic energy of a gas molecule,by what factor must you increase its momentum?

A)
B)2
C)2
D)4
E)16

Question 48

In the figure showing an isolated system,determine the character of the collision.The masses of the blocks,and the velocities before and after,are shown.The collision is

A)perfectly elastic.
B)partially inelastic.
C)completely inelastic.
D)characterized by an increase in kinetic energy.
E)not possible because momentum is not conserved.

Question 49

A firecracker explodes in midair and breaks up into many fragments.Which of the following statements are true regarding conditions immediately before and immediately after the explosion: I.The total momentum of the fragments is equal to the original momentum of the firecracker.
II.The total kinetic energy of the fragments is equal to the original kinetic energy of the firecracker.

A)Statement I only
B)Statement II only
C)Both Statement I and Statement II
D)Neither statement is true.

Question 50

A 5-kg ball collides inelastically head-on with a 10-kg ball,which is initially stationary.Which of the following statements is true? (There could be more than one correct choice.)

A)The magnitude of the change of velocity the 5-kg ball experiences is greater than that of the 10-kg ball.
B)The magnitude of the change of velocity the 5-kg ball experiences is less than that of the 10-kg ball.
C)The magnitude of the change of velocity the 5-kg ball experiences is equal to that of the 10-kg ball.
D)The magnitude of the change of the momentum of the 5-kg ball is equal to the magnitude of the change of momentum of the 10-kg ball.
E)Both balls lose all their momentum since the collision is inelastic.

Question 51

A rubber ball bounces off of a wall with an initial speed v and reverses its direction so its speed is v right after the bounce.As a result of this bounce,which of the following quantities of the ball are conserved? (There could be more than one correct choice.)

A)the kinetic energy of the ball
B)the momentum of the ball
C)both the momentum and the kinetic energy of the ball
D)None of the above quantities are conserved.

Question 52

How do the escape speeds for two rockets,the first weighing 20 N and the second weighing 20,000 N compare?

A)The escape speed for the lighter rocket is smaller than that for the heavier rocket.
B)The escape speed for the lighter rocket is the same as that for the heavier rocket.
C)The escape speed for the lighter rocket is greater than that for the heavier rocket.

Question 53

How much work would a child do while pulling a 12-kg wagon a distance of exerting a force?

A)95 J
B)52 J
C)67 J
D)109 J

Question 54

A railroad car collides with and sticks to an identical railroad car that is initially at rest.After the collision,the kinetic energy of the system

A)is the same as before.
B)is half as much as before.
C)is one third as much as before.
D)is one fourth as much as before.
E)is one quarter as much as before.

Question 55

On a horizontal frictionless air table,a puck runs into an ideal horizontal spring that is fastened to the table.The puck compresses the spring by 15 cm before coming to rest.During the compression process,which quantities are conserved?

A)only the momentum of the puck
B)only the kinetic energy of the puck
C)only the mechanical energy (kinetic plus potential)of the puck
D)the momentum and the mechanical energy of the puck
E)the momentum and the kinetic energy of the puck

Question 56

An egg falls from a bird's nest in a tree and feels no effects due to the air.As it falls,

A)only its kinetic energy is conserved.
B)only its momentum is conserved.
C)both its kinetic energy and its momentum are conserved.
D)only its mechanical energy is conserved.
E)both its mechanical energy and its momentum are conserved.

Question 57

Planet A has twice the mass of Planet B.From this information,what can we conclude about the escape speed for Planet A compared to that of Planet B?

A)The escape speed for Planet A must be twice as great as the escape speed from Planet B.
B)The escape speed for Planet A must be four times as great as the escape speed from Planet B.
C)The escape speed for Planet A is the same as the escape speed from Planet B.
D)The escape speed for Planet A is greater than the escape speed from Planet B, but we cannot say how much greater.
E)We cannot conclude anything about the escape speed for Planet A without knowing the radii of the two planets.

Question 58

If you want to double the momentum of a gas molecule,by what factor must you increase its kinetic energy?

A)
B)2
C)2
D)4
E)16

Question 59

If a quantity you calculated had units of kg ∙ m/s,what type of quantity could it be? (There could be more than one correct choice.)

A)momentum
B)kinetic energy
C)work
D)impulse
E)force

Question 60

Two objects of different masses have momentum of equal,non-zero magnitude.Which object has more kinetic energy?

A)the heavier object
B)the lighter object
C)They both have the same kinetic energy.

Question 61

What is the minimum energy needed to change the speed of a 1600-kg sport utility vehicle from 15.0 m/s to 40.0 m/s?

A)1.10 MJ
B)10.0 kJ
C)20.0 kJ
D)40.0 kJ
E)0.960 MJ

Question 62

Find the how much mechanical energy was converted to internal energy in the system box-surface-Earth when a box moves in a complete circle of radius on a uniform horizontal floor.The coefficient of kinetic friction between the floor and the box is 0.25,and the box weighs

A)190 J
B)0 J
C)1800 J
D)370 J

Question 63

A 1.0-kg object moving in a certain direction has a kinetic energy of 2.0 J.It hits a wall and comes back with half its original speed.What is the kinetic energy of this object at this point?

A)2.0 J
B)1.0 J
C)0.50 J
D)0.25 J
E)4.0 J

Question 64

A person carries a 25.0-N rock (the system)through the path shown in the figure,starting at point A and ending at point B.The total time from A to B is 1.50 min.How much work did the gravitational force exerted on the rock by Earth do on the rock between A and B?

A)625 J
B)20.0 J
C)275 J
D)75 J
E)0 J

Question 65

Matthew pulls his little sister Sarah along the horizontal ground in a wagon.He exerts a force on the wagon of 60.0 N at an angle of 37.0° above the horizontal.If he pulls her a distance of 12.0 m,how much work does Matthew do?

A)185 J
B)433 J
C)575 J
D)720 J

Question 66

How much kinetic energy does a 0.30-kg stone have if it is thrown at

A)290 J
B)580 J
C)440 J
D)510 J

Question 67

How much work must be done by frictional forces in slowing a 1000-kg car from to rest?

A)3.41 × 10⁵ J
B)2.73 × 10⁵ J
C)4.09 × 10⁵ J
D)4.77 × 10⁵ J

Question 68

A 10-kg dog is running with a speed of 5.0 m/s.What is the minimum work required to stop the dog in 2.40 s?

A)50 J
B)75 J
C)100 J
D)125 J

Question 69

It requires 0.30 kJ of work to fully drive a stake into the ground.If the average resistive force on the stake by the ground is how long is the stake?

A)0.36 m
B)0.23 m
C)0.31 m
D)0.41 m

Question 70

A 30-N box is pulled upward 6.0 m along the surface of a ramp that rises at 37° above the horizontal.How much work does the gravitational force exerted on the box by Earth do on the box during this process?

A)-1100 J
B)-110 J
C)-140 J
D)-180 J
E)120 J

Question 71

How fast must a 6.0-kg cat run to have a kinetic energy of 150 J?

Question 72

A traveler pulls on a suitcase strap at an angle 36° above the horizontal.The suitcase is the system.If of work are done by the strap while moving the suitcase a horizontal distance of what is the tension force that the strap exerts on the suitcase?

A)46 N
B)37 N
C)52 N
D)56 N

Question 73

When a car of mass accelerates from 10.0 m/s to some final speed,4.00 × 10⁵ J of work are done on it by the frictional force exerted on the car by the road's surface.Find this final speed.

A)28.0 m/s
B)22.4 m/s
C)25.2 m/s
D)30.8 m/s

Question 74

A crane lifts a 425 kg steel beam vertically upward a distance of How much work does the crane do on the beam if the beam accelerates upward at 1.8 m/s²? Neglect frictional forces.

A)4.7 × 10⁵ J
B)2.7 × 10⁵J
C)3.2 × 10⁵ J
D)4.0 × 10^{5 J}

Question 75

A stone (the system)with a mass of 1.0 kg is tied to the end of a light string which keeps it moving in a circle with a constant speed of 4.0 m/s on a perfectly smooth horizontal tabletop.The radius of the path is 0.60 m.How much work does the force exerted by the string do on the stone as it makes one-half of a complete circle?

A)100 J
B)3.8 J
C)0 J
D)40 J
E)80 J

Question 76

A 2.0-kg object (the system)is lifted vertically through 3.00 m by a constant 150-N force.How much work did Earth do on the object during this process?

Question 77

A person carries a 2.00-N pebble through the path shown in the figure,starting at point A and ending at point B.The total time from A to B is 6.75 min.How much work did the gravitational force exerted on the pebble by Earth do on the pebble between A and B?

A)30.0 J
B)-30.0 J
C)-56.0 J
D)56.0 J
E)-36.0 J

Question 78

A 500-kg elevator is pulled upward by a cable that exerts a constant force of 5500 N on the elevator for a distance of 50.0 m.The elevator is the system.
(a)What is the work done by the 5500-N force?
(b)What is the work done by the gravitational force?
(c)What is the net work done on the elevator?

Question 79

An object hits a wall and bounces back with half of its original speed.What is the ratio of the final kinetic energy to the initial kinetic energy of the object?

A)1/2
B)1/4
C)1/8
D)1/16

Question 80

A 1000-kg car is moving at 15 km/h.If a 2000-kg truck has 23 times the kinetic energy of the car,how fast is the truck moving?

A)51 km/h
B)72 km/h
C)61 km/h
D)41 km/h