Kinetic Energy and Work - Chapter No 6

Right Answers have been shown below in red color.

1. Which of the following is NOT a correct unit for work?

A. erg
B. ft·lb
C. watt
D. newton·meter
E. joule

2. Which of the following groups does NOT contain a scalar quantity?

A. velocity, force, power
B. displacement, acceleration, force
C. acceleration, speed, work
D. energy, work, distance
E. pressure, weight, time

3. A boy holds a 40-N weight at arm’s length for 10 s. His arm is 1.5 m above the ground. The work done by the force of the boy on the weight while he is holding it is:

A. 0
B. 6.1 J
C. 40 J
D. 60 J
E. 90 J

4. A crate moves 10 m to the right on a horizontal surface as a woman pulls on it with a 10-N force. Rank the situations shown below according to the work done by her force, least to greatest.

A. 1, 2, 3
B. 2, 1, 3
C. 2, 3, 1
D. 1, 3, 2
E. 3, 2, 1

5. An object moves in a circle at constant speed. The work done by the centripetal force is zero because:

A. the displacement for each revolution is zero
B. the average force for each revolution is zero
C. there is no friction
D. the magnitude of the acceleration is zero
E. the centripetal force is perpendicular to the velocity

6. An object of mass 1 g is whirled in a horizontal circle of radius 0.5 m at a constant speed of 2 m/s. The work done on the object during one revolution is:

A. 0
B. 1 J
C. 2 J
D. 4 J
E. 16 J

7. The work done by gravity during the descent of a projectile:

A. is positive
B. is negative
C. is zero
D. depends for its sign on the direction of the y axis
E. depends for its sign on the direction of both the x and y axes

8. A baseball is hit high into the upper bleachers of left field. Over its entire flight the work done by gravity and the work done by air resistance, respectively, are:

A. positive; positive
B. positive; negative
C. negative; positive
D. negative; negative
E. unknown since vital information is lacking

9. A line drive to the shortstop is caught at the same height as it was originally hit. Over its entire flight the work done by gravity and the work done by air resistance, respectively, are:

A. zero; positive
B. zero; negative
C. positive; negative
D. negative; positive
E. negative; negative

10. A 2-kg object is moving at 3 m/s. A 4-N force is applied in the direction of motion and then removed after the object has traveled an additional 5 m. The work done by this force is:

A. 12 J
B. 15 J
C. 18 J
D. 20 J
E. 38 J

11. A sledge (including load) weighs 5000 N. It is pulled on level snow by a dog team exerting a horizontal force on it. The coefficient of kinetic friction between sledge and snow is 0.05. How much work is done by the dog team pulling the sledge 1000 m at constant speed?

A. 2.5 × 104 J
B. 2.5 × 105 J
C. 5.0 × 105 J
D. 2.5 × 106 J
E. 5.0 × 106 J

12. Camping equipment weighing 6000 N is pulled across a frozen lake by means of a horizontal rope. The coefficient of kinetic friction is 0.05. The work done by the campers in pulling the equipment 1000 m at constant velocity is:

A. 3.1 × 104 J
B. 1.5 × 105 J
C. 3.0 × 105 J
D. 2.9 × 106 J
E. 6.0 × 106 J

13. Camping equipment weighing 6000 N is pulled across a frozen lake by means of a horizontal rope. The coefficient of kinetic friction is 0.05. How much work is done by the campers in pulling the equipment 1000 m if its speed is increasing at the constant rate of 0.20 m/s2 ?

A. −1.2 × 106 J
B. 1.8 × 105 J
C. 3.0 × 105 J
D. 4.2 × 105 J
E. 1.2 × 106 J

14. A 1-kg block is lifted vertically 1 m by a boy. The work done by the boy is about:


A. 1 ft · lb
B. 1 J
C. 10 J
D. 0.1 J
E. zero

15. A 0.50-kg object moves in a horizontal circular track with a radius of 2.5 m. An external force of 3.0 N, always tangent to the track, causes the object to speed up as it goes around. The work done by the external force as the mass makes one revolution is:

A. 24 J
B. 47 J
C. 59 J
D. 94 J
E. 120 J

16. A man pulls a 100-N crate up a frictionless 30◦ slope 5 m high, as shown. Assuming that the crate moves at constant speed, the work done by the man is:

A. −500 J
B. −250 J
C. 0
D. 250 J
E. 500 J

17. A man pushes an 80-N crate a distance of 5.0 m upward along a frictionless slope that makes an angle of 30◦ with the horizontal. His force is parallel to the slope. If the speed of the crate decreases at a rate of 1.5 m/s2, then the work done by the man is:

A. −200 J
B. 61 J
C. 140 J
D. 200 J
E. 260 J

18. A man pushes an 80-N crate a distance of 5.0 m upward along a frictionless slope that makes an angle of 30◦ with the horizontal. The force he exerts is parallel to the slope. If the speed of the crate is constant, then the work done by the man is:

A. −200 J
B. 61 J
C. 140 J
D. 200 J
E. 260 J

19. An 80-N crate slides with constant speed a distance of 5.0 m downward along a rough slope that makes an angle of 30◦ with the horizontal. The work done by the force of gravity is:

A. −400 J
B. −200 J
C. −69 J
D. 200 J
E. 400 J

20. A man pulls a sled along a rough horizontal surface by applying a constant force Fn at an angle θ above the horizontal. In pulling the sled a horizontal distance d, the work done by the man
is:

A. F d
B. F d cos θ
C. F d sin θ
D. F d/ cos θ
E. F d/ sin θ

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