Multiple Choice Practice – Work, Power and Energy
CEBDAEEAABBADDEDECEDDA
1.
The graph at the left represents the potential energy U
as a function of position r for a particle of mass m. If
the particle is released from rest at position ro, what
will its speed be at position 3ro?
e. The particle will never reach position 3ro.
2. A 10-meter long, vertical cannon is used to accelerate a 1.0-kg ball straight up into the air. A constant force
of 13.2 N is used to accelerate the bowling ball up the length of the cannon. What is the ball’s approximate
velocity as it leaves the cannon (assuming no energy loss to friction)?
a. 29 m/s
b. 16 m/s
c. 14 m/s
d. 9 m/s
e. 8 m/s
3.
The potential energy function U(x) is associated with
a conservative force F and described by the graph
given here. If a particle being acted upon by this force
has a kinetic energy of 1.0 J at position xo, what is
the particle’s kinetic energy at position x4?
(a) 6.0 J
(b) 7.0 J
(c) 2.0 J
(d) -2.0 J
(e) -7.0 J
4.
A mass of 2.0 kg is attached to the end of a light cord to make a
pendulum 5.0 m in length. The mass is raised to an angle of 53o relative
to the vertical, as shown, and released. The speed of the mass at the
bottom of its swing is:
(a) 60 m/s
(b) 7.7 m/s (c) 40 m/s (d) 6.3 m/s (e) 10 m/s
5. A block of wood, initially moving along a rough surface, is pushed with an applied horizontal force Fa that is
less than the friction force Ff. Which of the following statements is false?
(a) The Work being done by the applied force is negative.
(b) The net Work being done on the block is negative
(c) The block is slowing down
(d) The net Work being done on the box decreases its kinetic energy K
(e) There is an increase in internal energy due to friction
6. A 300 W electric wheelchair has a mass of 50 kg and carries its 50 kg occupant at constant velocity up a long
ramp. About how much time does it take the wheelchair to reach the top of the 10 m high ramp?
(a) 3 s
(b) 17 s
(c) 10 s
(d) 333 s
(e) 33 s
7. An object of mass m moves horizontally, increasing in speed from 0 to v in a time t. The power necessary to accelerate
the object during this time period is:
8. A bucket of water with a total weight of 50 N is lifted at constant velocity up a 10 m deep well. If it takes 20 s to raise
the bucket this distance, the power required to lift the bucket is:
(a) 25 W
(b) 25 J (c) 2.5 J(d) 500 J
(e) 500 W
9. A force F of strength 25 N acts on an object of mass 3 kg as it moves a distance of 4 m. If F is perpendicular to the 4 m
displacement, the work it does is equal to
(a) 0 J
(b) 60 J (c) 80 J
(d) 600 J
(e) 2400 J
10. Under the influence of a force, an object of mass 4 kg accelerates from 3 m/s to 6 m/s in 8 s. How much work was
done on the object during this time?
(a) 27 J
(b) 54 J (c) 72 J
(d) 96 J
(e) Cannot be determined from the info given
11. A box of mass m slides down a frictionless inclined plane of length L and vertical height h. What is the change in its
gravitational potential energy?
(a) –mgL
(b) –mgh
(c) –mgL/h
(d) –mgh/L
(e) –mghL
12. While a person lifts a book of mass 2 kg from the floor to a tabletop, 1.5 m above the floor, how much work does the
gravitational force do on the book?
(a) -30 J
(b) -15 J
(c) 0 J
(d) 15 J (e) 30 J
13. A block of mass 3.5 kg slides down a frictionless inclined plane of length 6.4 m that makes an angle of 30o with the
horizontal. If the block is released from rest at the top of the incline, what is its speed at the bottom?
(a) 5.0 m/s
(b) 5.7 m/s
(c) 6.4 m/s
(d) 8.0 m/s
(e) 10 m/s
14. A block of mass m slides from rest down an inclined plane of length s and height h. If F is the magnitude of the force
of kinetic friction acting on the block as it slides, then the kinetic energy of the block when it reaches the bottom of the
incline will be equal to
(a) mgh (b) mgh – Fh
(c) mgs – Fh
(d) mgh – Fs
(e) mgs – Fs
15. As a rock of mass 6 kg drops from the edge of a 40 m high cliff, it experiences air resistance, whose average strength
during the descent is 20 N. At what speed will the rock hit the ground?
(a) 8 m/s
(b) 10 m/s
(c) 12 m/s
(d) 16.3 m/s
(e) 23 m/s
16. A force of 200 N is required to keep an object sliding at a constant speed of 2 m/s across a rough floor. How much
power is being expended to maintain this motion?
(a) 50 W
(b) 100 W
(c) 200 W
(d) 400 W
(e) cannot be determined from the info given
17.
A block of weight mg = 100 N slides a distance of 5.0 m
down a 30o incline. How much work is done in the block by
gravity?
(a) 500 J
(b) 430 J
(c) 100 J
(d) 50 J
(e) 250 J
18. A block is attached to an ideal spring undergoes simple harmonic motion. The acceleration of the block has
its maximum magnitude at the point where
(A) the speed is the maximum
(B) the potential energy is the minimum
(C) the speed is a minimum
(D) the restoring force is the minimum
(E) the kinetic energy is the maximum
19. A block attached to an ideal spring undergoes simple harmonic motion about its equilibrium position (x= 0)
with amplitude A. What fraction of the total energy is in the form of kinetic energy when the block is at position
x = ½ A?
(A) 1/3
(B) 3/8
(C) ½
(D) 2/3
(E) ¾
20. Which of the following is/are characteristics of simple harmonic motion?
I. The acceleration is constant
II. The restoring force is proportional to the displacement
III. The frequency is independent of the amplitude
(a) II only
(B) I and II only
(C) I and III only
(D) II and III only
(E) I, II, and III
21. A simple pendulum is constructed by attaching a mass m to a thin rod of length l. The pendulum is pulled
back to some angle ϴ> 30o from the vertical and released. Which of the following techniques could be used to
change the frequency f of this pendulum?
I. Changing the mass m on the end of the pendulum
II. Changing the length l of the pendulum
III. Changing the angle ϴ from which the pendulum is released.
(A) I only
(B) I and II only
(C) II only
(D) II and III only
(E) I, II, and III
22. An enormous pendulum-driven clock, located on the earth, is set into motion by releasing its 10-m long
pendulum from a maximum angle of less than 10o relative to the vertical. At what approximate time t will the
pendulum have fallen to a perfectly vertical orientation?
(A)
(B)
(C)
(D)
(E)
23. A mass m is attached to the bottom of a string of negligible mass and length L to form a simple pendulum.
The mass is pulled back a small angle ϴ and released so that the pendulum swings back and forth with simple
harmonic motion. Which of the following statements is true of this pendulum?
(A) The acceleration of m is a minimum when displacement ϴ is a minimum
(B) The period of the pendulum varies as a function of m
(C) The kinetic energy of the pendulum is a maximum when its displacement is a maximum
(D) The frequency of the pendulum varies with angle ϴ
(E) The length of the string L has no effect on the period of the pendulum