Deck 7: Work and Kinetic Energy

Question 1

When you throw a pebble straight up with initial speed V,it reaches a maximum height H with 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 1

V

Question 2

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

Answer 2

They all travel the same distance in stopping.

Question 3

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.

Answer 3

Both do zero work.

Question 4

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 5

When you drop a pebble from height H,it reaches the ground with kinetic energy K if 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 6

Jill does twice as much work as Jack does and in half the time.Jill's power output is

A)the same as Jack's power output.
B)one-fourth as much as Jack's power output.
C)one-half as much as Jack's power output.
D)twice Jack's power output.
E)four times Jack's power output.

Question 7

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.

Question 8

When you drop a pebble from height H,it reaches the ground with speed V if 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 throw a baseball straight up.Compare the sign of the work done by gravity while the ball goes up with the sign of the work done by gravity 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 10

Two objects,one of mass m and the other of mass 2m,are dropped from the top of a building.If 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.

Question 11

If the force 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 12

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.Both objects encounter the same constant braking force,and 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 13

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 14

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 work done by Joe is equal to the amount of work done by Bob,but the average power exerted by Joe is greater than that of Bob.
B)The amount of work done by Joe is greater than the amount of work done by Bob,and the average power exerted by Joe is greater than that of Bob.
C)Bob and Joe exerted the same amount of work,and the average power of each cyclist was also the same.
D)The average power exerted by Bob and Joe was the same,but Joe exerted more work in getting there.

Question 15

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

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

Question 16

A force produces power P by doing work W in a time T.What power will be produced by 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 17

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 18

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 19

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 20

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 21

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

Question 22

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 23

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 24

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 gravity do on the box during this process?

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

Question 25

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 26

A person carries a 25.0-N rock 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 gravity 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 27

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 28

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

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

Question 29

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 30

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 31

When a car of mass
Accelerates from 10.0 m/s to some final speed,4.00 × 10⁵ J of work are done.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 32

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 33

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 gravity do on the rock 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 34

Find the net work done by friction on a box that 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)1,800 J
D)370 J

Question 35

A traveler pulls on a suitcase strap at an angle 36° above the horizontal.If
Of work are done by the strap while moving the suitcase a horizontal distance of
What is the tension in the strap?

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

Question 36

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 37

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 38

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 39

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 40

A stone 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 tension in 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 41

A 1000-kg car experiences a net force of 9500 N while slowing down from 30 m/s to 15.9 m/s. How far does it travel while slowing down?

A)34 m
B)31 m
C)37 m
D)41 m

Question 42

A sled having a certain initial speed on a horizontal surface comes to rest after traveling 10 m.If the coefficient of kinetic friction between the object and the surface is 0.20,what was the initial speed of the object?

A)9.8 m/s
B)6.3 m/s
C)3.6 m/s
D)7.2 m/s
E)8.9 m/s

Question 43

A driver,traveling at 22 m/s,slows down her 2000 kg truck to stop for a red light.What work is done on the truck by the friction force of the road?

A)-2.2 × 10⁴ J
B)-4.4 × 10⁴ J
C)-4.8 × 10⁵ J
D)-9.7 × 10⁵ J

Question 44

An ideal spring stretches by 21.0 cm when a 135-N object is hung from it.If instead you hang a fish from this spring,what is the weight of a fish that would stretch the spring by

A)199 N
B)91 N
C)145 N
D)279 N

Question 45

A 10-kg mass,hung by an ideal spring,causes the spring to stretch 2.0 cm.What is the spring constant (force constant)for this spring?

A)5.0 N/cm
B)49 N/cm
C)0.20 N/cm
D)20 N/m
E)0.0020 N/cm

Question 46

How large a net force is required to accelerate a 1600-kg SUV from rest to a speed of 25 m/s in a distance of 200 m?

A)1600 N
B)0 N
C)200 N
D)400 N
E)2500 N

Question 47

An ideal spring has a spring constant (force constant)of 2500 N/m.is stretched 4.0 cm.How much work is required to stretch the spring by 4.0 cm?

A)4.0 J
B)0.00 J
C)1.0 J
D)3.0 J
E)2.0 J

Question 48

A certain car traveling at 34.0 mph skids to a stop in 29 meters from the point where the brakes were applied.In approximately what distance would the car have stopped had it been going 105.4 mph?

A)279 m
B)158 m
C)90 m
D)51 m
E)29 m

Question 49

A 100-N force has a horizontal component of 80 N and a vertical component of 60 N.The force is applied to a cart on a level frictionless floor.The cart starts from rest and moves 2.0 m horizontally along the floor due to this force.What is the cart's final kinetic energy?

A)200 J
B)160 J
C)120 J
D)zero

Question 50

In a ballistics test,a 28-g bullet pierces a sand bag that is
Thick.If the initial bullet velocity was
And it emerged from the sandbag moving at
What was the magnitude of the friction force (assuming it to be constant)that the bullet experienced while it traveled through the bag?

A)130 N
B)38 N
C)13 N
D)1.3 N

Question 51

A child pulls on a wagon with a force of
If the wagon moves a total of
In
What is the average power delivered by the child?

A)17 W
B)21 W
C)22 W
D)26 W

Question 52

A stone is moving on a rough level surface.It has 24 J of kinetic energy,and the friction force on it is a constant 0.50 N.What is the maximum distance it can slide?

A)2.0 m
B)12 m
C)24 m
D)48 m

Question 53

On an alien planet,an object moving at 4.0 m/s on the horizontal ground comes to rest after traveling a distance of 10 m.If the coefficient of kinetic friction between the object and the surface is 0.20,what is the value of g on that planet?

A)4.0 m/s²
B)6.0 m/s²
C)8.0 m/s²
D)10 m/s²
E)12 m/s²

Question 54

A stone initially moving at 8.0 m/s on a level surface comes to rest due to friction after it travels 11 m.What is the coefficient of kinetic friction between the stone and the surface?

A)0.13
B)0.25
C)0.30
D)0.43
E)0.80

Question 55

The kinetic friction force that a horizontal surface exerts on a 60.0-kg object is 50.0 N.If the initial speed of the object is 25.0 m/s,what distance will it slide before coming to a stop?

A)15.0 m
B)30.0 m
C)375 m
D)750 m