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Work and Energy
Section Quiz: Power
Write the letter of the correct answer in the space provided.
______ 1. Which of the following refers to the rate at which energy is transferred?
a. work
b. kinetic energy
c. mechanical energy
d. power
______ 2. Which of the following refers to the rate at which work is done?
a. energy
b. kinetic energy
c. mechanical energy
d. power
______ 3. Which of the following is not a valid equation for power?
W
a. P t
Fd
b. P t
Fv
c. P t
d. P Fv
______ 4. The SI unit for power is
a. N•m.
b. J.
c. W.
d. hp.
______ 5. How much work can a motor with a power output of 25 W do in 1 s?
1
a. J
25
b. 1 J
c. 25 J
d. 25 W
______ 6. If a machine increases the distance over which work is done,
a. the force required to do the work is less.
b. the force required to do the work is greater.
c. the force required to do the work is the same.
d. the amount of work done is increased.
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Work and Energy continued
______ 7. If a machine decreases the distance over which work is done,
a. the force the machine applies is less.
b. the force the machine applies is greater.
c. the force the machine applies is the same.
d. the amount of work done is decreased.
______ 8. A 100 W light bulb
a. converts 100 J of kinetic energy to potential energy each second.
b. converts 100 J of potential energy to kinetic energy each second.
c. converts 100 J of mechanical energy to nonmechanical energy each
second.
d. converts 100 J of electrical energy to other forms of energy each
second.
9. Describe the relationship between energy, time, and power.
10. An engine uses 29 kN of force to power a car at an average speed of 7.5 m/s.
What is the average power output of the engine?
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TEACHER RESOURCE
5 Work and Energy
6 Momentum and Collisions
POWER
CONSERVATION OF MOMENTUM
1.
2.
3.
4.
9.
d
5. c
d
6. a
c
7. b
c
8. d
Power measures the amount of energy
that is transferred from one object to
another or transformed to other forms
of energy in a given time interval.
10. 220 kW
Given
F 29 kN 2.9 104 N
v 7.5 m/s
Solution
P Fv (2.9 104 N)(7.5 m/s) 2.2 105 W 220 kW
6 Momentum and Collisions
1.
2.
3.
4.
9.
d
5. d
c
6. c
b
7. d
d
8. c
The magnitude of the momentum of
the slower ball increases, while the
magnitude of the momentum of the
faster ball decreases by the same
amount. Both balls reverse direction in
the collision. The total momentum of
the system does not change.
10. 1.9 m/s
Given
m1 55 kg
v1,i 2.0 m/s
m2 2.0 kg
v2,i 0 m/s
v1, f v2, f
MOMENTUM AND IMPULSE
b
5. b
c
6. c
a
7. c
c
8. d
Impulse is the product of the force
acting on an object and the time
interval in which the force acts on
an object. The impulse-momentum
theorem states that the impulse on an
object is equal to the change in the
object’s momentum.
10. 9.0 106 kg•m/s
Given
m 1.0 104 kg
vi 1.2 103 m/s
F 25 kN 2.5 104 N
t 2.0 min 120 s
Solution
m1v1,i m2v2,i m1v1, f m2v2, f
m1v1,i m1v1, f m2v1, f
m1v1,i (m1 m2)v1, f
m1v1,i
v1, f (m1 m2)
1.
2.
3.
4.
9.
Solution
pi mvi (1.0 104 kg)(1.2 103 m/s) 1.2 107 kg•m/s
Ft p pf pi
pf Ft pi
pf (2.5 104 N)(120 s) (1.2 107 kg•m/s) 9.0 106 kg•m/s
(55 kg)(2.0 m/s)
v1, f 1.9 m/s
(55 kg 2.0 kg)
6 Momentum and Collisions
ELASTIC AND INELASTIC COLLISIONS
1.
2.
3.
4.
9.
d
5. d
b
6. a
a
7. b
b
8. d
An inelastic collision is any collision in
which some kinetic energy is converted
to other forms of energy so that the
total kinetic energy is not conserved. A
perfectly inelastic collision is a special
case in which the objects in the collision stick together and move as a single
object after the collision.
10. 1.2 m/s to the right
Given
m1 0.16 kg
v1,i 1.2 m/s
m2 0.16 kg
v2,i 0.85 m/s
v1,f 0.85 m/s
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Holt Physics
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Answer Key