Question 1

How many joules of energy are used by a 1.0-hp motor that runs for 1.0 hour? (1 hp = 746 W)

Accepted Answer

A)  3.6 kJ 
B)  2.7 MJ 
C)  45 kJ 
D)  4.8 J 
A)  3.6 kJ 
B)  2.7 MJ 
C)  45 kJ 
D)  4.8 J

Question 2

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?

Accepted Answer

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

Question 3

A solid uniform sphere of mass 120 kg and radius 1.7 m starts from rest and rolls without slipping down an inclined plane of vertical height 5.3 m. What is the angular speed of the sphere at the bottom of the inclined plane?

Accepted Answer

A)  5.1 rad/s 
B)  8.7 rad/s 
C)  9.7 rad/s 
D)  6.1 rad/s 
A)  5.1 rad/s 
B)  8.7 rad/s 
C)  9.7 rad/s 
D)  6.1 rad/s

Question 4

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?

Accepted Answer

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

Question 5

A solid uniform disk of diameter 3.20 m and mass 42 kg rolls without slipping to the bottom of a hill, starting from rest. If the angular speed of the disk is 4.27 rad/s at the bottom, how high did it start on the hill?

Accepted Answer

A)  3.57 m 
B)  2.68 m 
C)  3.14 m 
D)  4.28 m 
A)  3.57 m 
B)  2.68 m 
C)  3.14 m 
D)  4.28 m

Question 6

A typical incandescent light bulb consumes 75 W of power and has a mass of 30 g. You want to save electrical energy by dropping the bulb from a height great enough so that the kinetic energy of the bulb when it reaches the floor will be the same as the energy it took to keep the bulb on for 1.0 hour. From what height should you drop the bulb, assuming no air resistance and constant g?

Accepted Answer

The answer of A typical incandescent light bulb consumes 75...

Question 7

A crane lifts a 425 kg steel beam vertically upward a distance of $95 \mathrm {~m} .$ How much work does the crane do on the beam if the beam accelerates upward at 1.8 m/s2? Neglect frictional forces.

Accepted Answer

A)  4.7 × 105 J 
B)  2.7 × 105J 
C)  3.2 × 105 J 
D)  4.0 × 105 J 
A)  4.7 × 105 J 
B)  2.7 × 105J 
C)  3.2 × 105 J 
D)  4.0 × 105 J

Question 8

A 30-N stone is dropped from a height of 10 m and strikes the ground with a speed of 13 m/s. What average force of air friction acted on the stone as it fell?

Accepted Answer

A)  4.1 N 
B)  2.9 N 
C)  0.13 kN 
D)  7.2 N 
E)  1.2 N 
A)  4.1 N 
B)  2.9 N 
C)  0.13 kN 
D)  7.2 N 
E)  1.2 N

Question 9

A frictionless simple pendulum, with a small but dense 4.4-kg mass at the end and a length of 75 cm, is released from rest at an angle of 50° with the vertical.
(a) To what height above its lowest point does the mass swing on the other side?
(b) What is the speed of the mass at the bottom of the swing?

Accepted Answer

(a) 27 cm

Question 10

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?

Accepted Answer

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 force of gravity 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. 
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 force of gravity 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 11

Two simple pendulums of equal length l = 0.45 m are suspended from the same point. The pendulum bobs are small solid steel spheres. The first bob is drawn back to make a 35° angle with the vertical, while the other one is left hanging at rest. If the first bob has a mass of 0.25 kg and the second has a mass of $0.54 \mathrm {~kg} \text {, }$ how high will the second bob rise above its initial position when struck elastically by the first bob after it is released?

Accepted Answer

A)  3.3 cm 
B)  2.7 cm 
C)  3.9 cm 
D)  4.4 cm 
A)  3.3 cm 
B)  2.7 cm 
C)  3.9 cm 
D)  4.4 cm

Question 12

A 340-g air track cart traveling at 1.25 m/s suddenly collides elastically with a stationary 300-g cart. What is the speed of the 300-g cart just after the collision?

Accepted Answer

A)  0.0781 m/s 
B)  1.33 m/s 
C)  0.625 m/s 
D)  1.25 m/s 
E)  0.664 m/s 
A)  0.0781 m/s 
B)  1.33 m/s 
C)  0.625 m/s 
D)  1.25 m/s 
E)  0.664 m/s

Question 13

A heavy rock and a light rock are dropped from the same height and experience no significant air resistance as they fall. Which of the following statements about these rocks are correct? (There could be more than one correct choice.)

Accepted Answer

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, both rocks 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. 
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, both rocks 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 14

How many joules of energy are used by a 2.0 hp motor that runs for 1.0 hour? (1 hp = 746 W)

Accepted Answer

The answer of How many joules of energy are used...

Question 15

To drive a typical car at 40 mph on a level road for one hour requires about 3.2 × 107 J of energy. Suppose we tried to store this much energy in a spinning, solid, uniform, cylindrical flywheel. A large flywheel cannot be spun too fast or it will fracture. If we used a flywheel of diameter 1.2 m and mass 400 kg, what angular speed would be required to store 3.2 × 107 J?

Accepted Answer

A)  1800 rad/s 
B)  3600 rad/s 
C)  940 rad/s 
D)  530 rad/s 
E)  5500 rad/s 
A)  1800 rad/s 
B)  3600 rad/s 
C)  940 rad/s 
D)  530 rad/s 
E)  5500 rad/s

Question 16

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

Accepted Answer

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

Question 17

What is the minimum energy needed to lift a 1.0-kg rocket to a height of 200 km and to give it a speed of 8.0 km/s at that height? (Neglect air resistance and the small decrease in g over that distance.)

Accepted Answer

A)  34 TJ 
B)  34 kJ 
C)  34 MJ 
D)  34 GJ 
E)  34 J 
A)  34 TJ 
B)  34 kJ 
C)  34 MJ 
D)  34 GJ 
E)  34 J

Question 18

Rita raises a 10kg package to a height of 2.5 m in 2.0 s.
(a) How much work did she do on the package?
(b) How much power was expended on the package?
(c) If she were to raise the package in 1.0 s rather than 2.0 s, how do the work and power change?

Accepted Answer

(a) 0.25 Kj (b) 0.12

Question 19

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?

Accepted Answer

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. 
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 20

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?

Accepted Answer

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

Exam 10: Energy and Work

How many joules of energy are used by a 1.0-hp motor that runs for 1.0 hour? (1 hp = 746 W)

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 solid uniform sphere of mass 120 kg and radius 1.7 m starts from rest and rolls without slipping down an inclined plane of vertical height 5.3 m. What is the angular speed of the sphere at the bottom of the inclined plane?

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 solid uniform disk of diameter 3.20 m and mass 42 kg rolls without slipping to the bottom of a hill, starting from rest. If the angular speed of the disk is 4.27 rad/s at the bottom, how high did it start on the hill?

A crane lifts a 425 kg steel beam vertically upward a distance of 95 m.95 \mathrm {~m} .95 m. How much work does the crane do on the beam if the beam accelerates upward at 1.8 m/s2? Neglect frictional forces.

A 30-N stone is dropped from a height of 10 m and strikes the ground with a speed of 13 m/s. What average force of air friction acted on the stone as it fell?

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 340-g air track cart traveling at 1.25 m/s suddenly collides elastically with a stationary 300-g cart. What is the speed of the 300-g cart just after the collision?

A heavy rock and a light rock are dropped from the same height and experience no significant air resistance as they fall. Which of the following statements about these rocks are correct? (There could be more than one correct choice.)

How many joules of energy are used by a 2.0 hp motor that runs for 1.0 hour? (1 hp = 746 W)

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

What is the minimum energy needed to lift a 1.0-kg rocket to a height of 200 km and to give it a speed of 8.0 km/s at that height? (Neglect air resistance and the small decrease in g over that distance.)

Rita raises a 10kg package to a height of 2.5 m in 2.0 s. (a) How much work did she do on the package? (b) How much power was expended on the package? (c) If she were to raise the package in 1.0 s rather than 2.0 s, how do the work and power change?

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?

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A crane lifts a 425 kg steel beam vertically upward a distance of $95 \mathrm {~m} .$ How much work does the crane do on the beam if the beam accelerates upward at 1.8 m/s²? Neglect frictional forces.