Deck 6: Work and Energy

Question 1

The net force acting on a 6.0-kg object is given by F_x = (12 - x) N, where F_x is in newtons and x is in meters. How much work is done on the object as it moves from x = 0 to x = 12 m?

A) 120 J
B) 72 J
C) 36 J
D) 18 J

Answer 1

72 J

Question 2

I use a rope 1.00-m-long to swing a 1.00-kg weight around my head. The tension in the rope is 20.0 N. In half a revolution how much work is done by the rope on the weight?

A) 20.0 J
B) 31.4 J
C) 123 J
D) 0

Answer 2

0

Question 3

In 1908 there was a huge explosion referred to as the Tunguska event which occurred in Siberia. Apparently this was caused by a very large meteorite, a small asteroid, or a comet colliding with the Earth. If the energy released, estimated at J, were from the kinetic energy of the object, what would have been its approximate mass if its speed had been m/s?

A)
B)
C)
D)

Answer 3

Question 4

The area under the force-displacement curve represents:

A) area.
B) work.
C) force.
D) coefficient of static friction.

Question 5

A horizontal force of 200 N is applied to a 55-kg cart across a 10 m level surface. If the cart accelerates at 3.0 m/s², then what is the work done by the force of friction as it acts to retard the motion of the cart?

A) "-900 J"
B) "-175 J"
C) "-350 J"
D) "-700 J"

Question 6

A horizontal force of 100 N is applied to move a 45-kg cart across a 5.0-m level surface. What work is done by the 100-N force?

A) 405 J
B) 500 J
C) 900 J
D) 4500 J

Question 7

The net force acting on a 12.6-kg object is given by F_x = (8 - x) N, where F_x is in newtons and x is in meters. How much work is done on the object as it moves from x = 0 to x = 6 m?

A) 64 J
B) 30 J
C) 28 J
D) 24 J

Question 8

A rock is thrown straight up with an initial velocity of 20.0 m/s. Ignore energy lost to air friction. How high will the rock rise?

A) 41.0 m
B) 10.2 m
C) 20.4 m
D) 11.5 m

Question 9

A 1200-kg automobile moving at 25 m/s has the brakes applied with a deceleration of 5.0 m/s². How far does the car travel before it stops?

A) 39 m
B) 31 m
C) 55 m
D) 63 m

Question 10

The unit of work, joule, is dimensionally the same as:

A) newton/second.
B) newton/kilogram.
C) newton-second.
D) newton-meter.

Question 11

A very light cart holding a 300-N box is moved at constant velocity across a 15-m level surface. What is the total work done in the process?

A) 4500 J
B) 1/20 J
C) 20 J
D) zero

Question 12

A 5.00 kg ball falls from a 2.00 m-high shelf. Just before hitting the floor, what will be its kinetic energy? (g = 9.80 m/s² and assume air resistance is negligible)

A) 98.0 J
B) 49.0 J
C) 19.6 J
D) 10.0 J

Question 13

Rupel pushes a box 4.00 m by applying a 25.0-N horizontal force. What work does she do?

A) 10.0 J
B) 100 J
C) 125 J
D) 550 J

Question 14

A force of 200 N is applied to a 50-kg mass in the direction of motion for a distance of 6.0 m, and then the force is increased to 300 N for the next 5.0 m. For the 11 m of travel, how much work is done by the varying force?

A) "2700 J"
B) "1500 J"
C) "2400 J"
D) "-1200 J"

Question 15

A satellite is held in orbit by a 3000-N gravitational force. Each time the satellite completes an orbit of circumference 80,000 km, the work done on it by gravity is:

A) 2.4 *10⁸ J
B) 2.4 *10¹¹ J
C) 9.6 *10¹¹ J
D) 0

Question 16

What is the minimum amount of energy required for a 70.0-kg climber carrying a 20.0-kg pack to climb Mt. Everest, which is 8850 m high?

A) 8.67 MJ
B) 7.81 MJ
C) 4.41 MJ
D) 0.900 MJ

Question 17

What is the kinetic energy of a 0.160-kg ball thrown at 40.0 m/s (90.0 mph)?

A) 54.0 J
B) 64.0 J
C) 108 J
D) 128 J
E) newton-meter.

Question 18

If during a given physical process the only force acting on an object is friction, which of the following must be assumed in regard to the object's kinetic energy?

A) decreases
B) increases
C) remains constant
D) cannot tell from the information given

Question 19

The work done by static friction can be:

A) positive.
B) negative.
C) zero.
D) Any of the above.

Question 20

A golf ball hits a wall and bounces back at 3/4 the original speed. What part of the original kinetic energy of the ball did it lose in the collision?

A) 1/4
B) 3/8
C) 7/16
D) 9/16

Question 21

Two blocks are released from the top of a building. One falls straight down while the other slides down a smooth ramp. If all friction is ignored, which one is moving faster when it reaches the bottom?

A) The block that went straight down.
B) The block that went down the ramp.
C) They both will have the same speed.
D) Insufficient information to work the problem.

Question 22

A professional skier reaches a speed of 39.6 m/s on a 30 $\degree$ ski slope. Ignoring friction, what was the minimum distance along the slope the skier would have had to travel, starting from rest?

A) 110 m
B) 160 m
C) 320 m
D) 640 m

Question 23

When an object is dropped from a tower, what is the effect of the air resistance as it falls?

A) It does positive work.
B) It increases the object's kinetic energy.
C) It increases the object's potential energy.
D) None of the above choices are valid.

Question 24

A 2.00-kg ball has zero potential and kinetic energy. Maria drops the ball into a 20.0-m deep well. After the ball comes to a stop in the mud, the sum of its potential and kinetic energy is:

A) "392 J."
B) "-392 J."
C) "784 J."
D) "zero."

Question 25

A bobsled makes a run down an ice track starting at 66 m vertical distance up the hill. If there is no friction, what is the velocity at the bottom of the hill?

A) 27 m/s
B) 36 m/s
C) 44 m/s
D) 54 m/s

Question 26

A 10.0-kg box starts at rest and slides 6.0 m down a ramp inclined at an angle of 10 $\degree$ with the horizontal. If there is no friction between the ramp surface and crate, what is the velocity of the crate at the bottom of the ramp? (g = 9.8 m/s²)

A) 6.1 m/s
B) 3.5 m/s
C) 10.7 m/s
D) 4.5 m/s

Question 27

An 80,000-kg airliner is flying at 900 km/h at a height of 8.00 km. What is its total energy (kinetic + potential) if the total was 0 when the airliner was at rest on the ground?

A) 250 MJ
B) 478 MJ
C) 8770 MJ
D) 10,300 MJ

Question 28

A baseball catcher puts on an exhibition by catching a 0.15-kg ball dropped from a helicopter at a height of 91 m. What is the speed of the ball just before it hits the catcher's glove 1.0 m above the ground? (g = 9.8 m/s² and ignore air resistance)

A) 84 m/s
B) 38 m/s
C) 42 m/s
D) 19 m/s

Question 29

As an object is lowered into a deep hole in the surface of the Earth, which of the following must be assumed in regard to its potential energy?

A) It increases.
B) It decreases.
C) It remains constant.
D) One cannot tell from the information given.

Question 30

A simple pendulum, 2.0 m in length, is released by a push when the support string is at an angle of 25 $\degree$ from the vertical. If the initial speed of the suspended mass is 3.0 m/s when at the release point, to what maximum angle will it move in the second half of its swing?

A) 36 $\degree$
B) 30 $\degree$
C) 19 $\degree$
D) 47 $\degree$

Question 31

A simple pendulum, 2.0 m in length, is released with a push when the support string is at an angle of 25 $\degree$ from the vertical. If the initial speed of the suspended mass is 2.0 m/s when at the release point, what is its speed at the bottom of the swing? (g = 9.8 m/s²)

A) 2.3 m/s
B) 2.6 m/s
C) 2.8 m/s
D) 0.5 m/s

Question 32

Old Faithful geyser in Yellowstone Park shoots water hourly to a height of 30 m. With what velocity does the water leave the ground?

A) 7.0 m/s
B) 14 m/s
C) 24 m/s
D) 28 m/s

Question 33

Samantha pushes a 60-N crate up a ramp 20.0 m in length and inclined at 10 $\degree$ with the horizontal. What potential energy change does the crate experience?

A) 1200 J
B) 210 J
C) 600 J
D) 300 J

Question 34

A 15.0-kg crate, initially at rest, slides down a ramp 4.0 m long and inclined at an angle of 20 $\degree$ with the horizontal. If there is no friction between ramp surface and crate, what is the kinetic energy of the crate at the bottom of the ramp? (g = 9.8 m/s²)

A) 200 J
B) 690 J
C) 10 J
D) 100 J

Question 35

A pole-vaulter clears 5.00 m. With what speed does he strike the mat in the landing area?

A) 2.70 m/s
B) 9.90 m/s
C) 10.8 m/s
D) 21.6 m/s

Question 36

A simple pendulum, 2.00 m in length, is released from rest when the support string is at an angle of 35.0 $\degree$ from the vertical. What is the speed of the suspended mass at the bottom of the swing? (g = 9.80 m/s² and ignore air resistance)

A) 0.941 m/s
B) 1.88 m/s
C) 2.66 m/s
D) 1.33 m/s

Question 37

A 2.00 kg-ball has zero kinetic and potential energy. Ernie drops the ball into a 10.0-m deep well. Just before the ball hits the bottom, the sum of its kinetic and potential energy is:

A) "zero."
B) "196 J."
C) "-196 J."
D) "392 J."

Question 38

Is it possible for the total mechanical energy of a moving particle to be negative?

A) No, because a moving particle has positive kinetic energy.
B) No, because potential energy cannot have a value more negative than the value of the positive kinetic energy of the particle.
C) Only if friction is involved.
D) Yes

Question 39

A baseball outfielder throws a baseball of mass 0.15 kg at a speed of 30 m/s and initial angle of 30 $\degree$ . What is the kinetic energy of the baseball at the highest point of the trajectory? Ignore air friction.

A) zero
B) 51 J
C) 92 J
D) 120 J

Question 40

A hill is 200 m long and makes an angle of 12 $\degree$ with the horizontal. As a 50-kg jogger runs up the hill, how much work does gravity do on the jogger?

A) "98,000 J"
B) "-20,000 J"
C) "20,000 J"
D) "zero"

Question 41

A Hooke's law spring is compressed 12.0 cm from equilibrium and the potential energy stored is 36.0 J. What is the spring constant in this case?

A) 10,000 N/m
B) 5000 N/m
C) 1200 N/m
D) The correct answer is not given.

Question 42

When a Hooke's law spring is stretched a distance 3x, how much is the increase in energy stored in it from when it was stretched a distance x? Give your answer in terms of a multiple of the energy stored in the spring when it is stretched a distance x.

A) It is 3 times as much.
B) It is 8 times as much.
C) It is 4 times as much.
D) It is 9 times as much.

Question 43

Which of the following is an example of a nonconservative force?

A) gravity
B) the force from a Hooke's law spring
C) friction
D) Both choices A and B are valid.

Question 44

A 50-N crate is pulled up a 5.0-m inclined plane by a worker at constant velocity. If the plane is inclined at an angle of 37 $\degree$ to the horizontal and there exists a constant frictional force of 20 N between the crate and the surface, what is the force applied by the worker?

A) zero
B) 50 N
C) 30 N
D) 40 N

Question 45

Which of the following is that form of energy associated with an object's location in a conservative force field?

A) potential
B) thermal
C) bio-chemical
D) kinetic

Question 46

The SI units for k, the spring constant, are equivalent to:

A) J
B) J / N
C) kg / s²
D) none of the above

Question 47

By how much is the energy stored in a Hooke's law spring increased when its stretch is increased from 4.00 cm to 8.00 cm?

A) 100%
B) 200%
C) 300 %
D) The correct answer is not given.

Question 48

A 2000-kg ore car rolls 50.0 m down a frictionless 10.0 $\degree$ incline. If there is a horizontal spring at the end of the incline, what spring constant is required to stop the ore car in a distance of 2.00 m?

A) 340 kN/m
B) 68.1 kN/m
C) 1700 kN/m
D) 85.1 kN/m

Question 49

In a problem using energy considerations to solve for the speed of a ball thrown from the top of a building when it strikes the ground below, where should the potential energy have its zero value?

A) It should be at the level from where the ball is thrown.
B) It should be at the ground level where the ball hits.
C) It should be slightly below ground level so the potential energy is always positive.
D) It doesn't matter since only differences in potential energy matter in solutions.

Question 50

An amount of work equal to 3.0 J is required to compress the spring in a spring-gun. What is the "launch speed" of a 15 g marble?

A) 14 m/s
B) 15 m/s
C) 18 m/s
D) 20 m/s

Question 51

A Hooke's law spring is mounted horizontally over a frictionless surface. The spring is then compressed a distance d and is used to launch a mass m along the frictionless surface. What compression of the spring would result in the mass attaining double the kinetic energy received in the above situation?

A) 1.41d
B) 1.73d
C) 2.00d
D) 4.00d

Question 52

A pendulum consists of a mass m suspended from a string of length L. When the pendulum is swinging, how much greater is the mass's potential energy when the string is displaced from the vertical by the angle than when the mass is at the lowest position?

A)
B)
C)
D)

Question 53

Which of the following is that form of energy associated with an object's motion?

A) potential
B) thermal
C) bio-chemical
D) kinetic

Question 54

Three different-mass projectiles are launched at different angles of elevation from the top of a building. Each particle has the same initial kinetic energy. Which particle has the greatest speed just as it impacts with the ground?

A) The one launched at the highest angle of elevation.
B) The one with the highest mass.
C) The one with the lowest mass.
D) They all will have the same speed on impact.

Question 55

Three different-mass projectiles are launched at different angles of elevation from the top of a building. Each particle has the same initial kinetic energy. Which particle has the greatest kinetic energy just as it impacts with the ground?

A) The one launched at the highest angle of elevation.
B) The one with the highest mass.
C) The one with the lowest mass.
D) They all will have the same kinetic energy on impact.

Question 56

Which of the following is not true about potential energy?

A) Potential energy is stored energy.
B) Potential energy is related to position.
C) Potential energy is a scalar quantity.
D) Potential energy has direction.

Question 57

A Hooke's law spring is compressed 12.0 cm from equilibrium, and the potential energy stored is 36.0 J. What compression (as measured from equilibrium) would result in 100 J being stored in this case?

A) 20.0 cm
B) 14.1 cm
C) 13.6 cm
D) The correct answer is not given.

Question 58

A Hooke's law spring is mounted horizontally over a frictionless surface. The spring is then compressed a distance d and is used to launch a mass m along the frictionless surface. What compression of the spring would result in the mass attaining double the speed received in the above situation?

A) 1.41d
B) 1.73d
C) 2.00d
D) 4.00d

Question 59

A worker pushes a sled with a force of 40 N over a level distance of 6.0 m. If a frictional force of 16 N acts on the wheelbarrow in a direction opposite to that of the worker, what total work is done on the wheelbarrow?

A) 240 J
B) 216 J
C) 144 J
D) 96 J

Question 60

A spring with spring constant k is used to launch a mass m up a frictionless inclined plane having angle of elevation . What is the maximum height reached above the starting elevation of the mass during the motion of the mass if the spring is compressed a distance d before launch?

A)
B)
C)
D)

Question 61

The unit of power, watt, is dimensionally the same as:

A) joule-second.
B) joule/second.
C) joule-meter.
D) joule/meter.

Question 62

A girl and her bicycle have a total mass of 40 kg. At the top of the hill her speed is 5.0 m/s. The hill is 10 m high and 100 m long. If the force of friction as she rides down the hill is 24 N, what is her speed at the bottom?

A) 5.0 m/s
B) 10 m/s
C) 11 m/s
D) She stops before she reaches the bottom.

Question 63

A 20-N crate starting at rest slides down a rough 5.0-m long ramp, inclined at 25 $\degree$ with the horizontal. 30 J of energy is lost to friction. What will be the speed of the crate at the bottom of the incline?

A) 0.98 m/s
B) 2.1 m/s
C) 3.5 m/s
D) 4.7 m/s

Question 64

How fast would a 1000-kg car be traveling if it had a kinetic energy equal to 1000 Calories?

A) 91 m/s
B) 2.9 m/s
C) 12 m/s
D) 8 m/s

Question 65

A parachutist of mass 50.0 kg jumps out of an airplane at a height of 800 m. The parachute deploys, and she lands on the ground with a speed of 5.0 m/s. How much energy was lost to air friction during this jump?

A) 49,400 J
B) 98,700 J
C) 391,000 J
D) 489,000 J

Question 66

The quantity of work equal to one joule is also equivalent to which of the following?

A) watt
B) watt /s
C) watt * s
D) watt /s²

Question 67

Yuri, a Russian weightlifter, is able to lift 300 kg a distance 2.00 m in 2.00 s. What is his power output?

A) 500 W
B) 2.45 kW
C) 2.94 kW
D) 9.80 kW

Question 68

A baseball catcher puts on an exhibition by catching a 0.150-kg ball dropped from a helicopter at a height of 100 m above the catcher. If the catcher "gives" with the ball for a distance of 0.500 m while catching it, what average force is exerted on the mitt by the ball? (g = 9.80 m/s²)

A) 78 N
B) 119 N
C) 197 N
D) 295 N

Question 69

A 66-kg woman runs up a flight of stairs having a rise of 4.0 m in a time of 4.2 s. What average power did she supply?

A) 380 W
B) 560 W
C) 620 W
D) 670 W

Question 70

A Hooke's law spring is compressed a distance d and is used to launch a mass m vertically to a height h above its starting position. Under double the compression, the spring is now used to launch the mass. How high does the mass now rise above its starting position?

A) 2h
B) 1.41h
C) 3h
D) 4h

Question 71

I drop a 60-g golf ball from 2.0 m high. It rebounds to 1.3 m. How much energy is lost?

A) 0.29 J
B) 0.41 J
C) 0.88 J
D) 1.0 J

Question 72

An automobile delivers 30.0 hp to its wheels when moving at a constant speed of 26.0 m/s. What is the resistance force on the automobile at this speed? (1 hp = 746 watts)

A) 18,600 N
B) 410,000 N
C) 1020 N
D) 861 N

Question 73

Adisa pulls a 50-N crate up a 5.0-m long inclined plane at a constant velocity. If the plane is inclined at an angle of 37 $\degree$ to the horizontal and there is a constant force of friction of 10 N between the crate and the surface, what is the net change in potential energy of the crate?

A) "120 J"
B) "-120 J"
C) "250 J
D) "150 J"

Question 74

A Hooke's law spring is compressed a distance d and is used to launch a mass m vertically to a height h above its starting position. Under the same compression d, the spring is now used to launch a mass of 2m. How high does this second mass rise?

A) h
B) h/2
C) h/1.41
D) h/4

Question 75

A pile driver drives a post into the ground. The mass of the pile driver is 2500 kg, and it is dropped through a height of 8.0 m on each stroke. If the resisting force of the ground is 2.0 * 10⁶ N, how far is the post driven in on each stroke?

A) 4.9 cm
B) 9.9 cm
C) 16 cm
D) 49 cm

Question 76

The rate at which work is done is equivalent to which of the following?

A) increase in potential energy
B) thermal energy
C) potential energy
D) power

Question 77

A block is projected with speed v across a horizontal surface and slides to a stop due to friction. The same block is then projected with the same speed v up an incline where it slides to a stop due to friction. In which case did the total mechanical energy of the block decrease the least?

A) This problem cannot be solved since it was not indicated whether the horizontal surface and the incline both had the same coefficient of kinetic friction.
B) The case on the horizontal surface had the least decrease in total mechanical energy.
C) The case on the inclined surface had the least decrease in total mechanical energy.
D) In both cases the decrease in mechanical energy was the same.

Question 78

A girl and her bicycle have a total mass of 40.0 kg. At the top of the hill her speed is 5.0 m/s, and her speed doubles as she rides down the hill. The hill is 12.0 m high and 100 m long. How much kinetic energy and potential energy is lost to friction?

A) 2420 J
B) 3200 J
C) 2000 J
D) 3920 J

Question 79

A Hooke's law spring is compressed a distance d and is used to launch a particle of mass m vertically to a height h above its starting position. Under double the compression, the spring is now used to launch a particle of mass 2 m. How high does the second mass rise above its starting position?

A) h
B) 2h
C) 3h
D) 4h

Question 80

Preston pushes a wheelbarrow weighing 500 N to the top of a 50.0-m ramp, inclined at 20.0 $\degree$ with the horizontal and leaves it. Tamara accidentally bumps the wheelbarrow. It slides back down the ramp, during which a 60.0-N frictional force acts on it over the 50.0 m. What is the wheelbarrow's kinetic energy at the bottom at of the ramp? (g = 9.8 m/s²)

A) 5550 J
B) 6550 J
C) 8150 J
D) 13,100 J