KEY KEY KEY__
NOTE : g = 9.8 m / s2
Energy Unit Review
1. Which of the following has the largest momentum relative to Earth?
A. a person walking down the street
B. a truck and horse trailer traveling on the highway
C. a large truck parked
D. a school building
E. a space shuttle in its hangar
2. A truck is going the speed limit on the highway. We magically add a load of hay, to the truck,
doubling its mass, while it continues at its original speed. The truck’s momentum is___.
A. quadrupled
B. doubled
C. the same as before
3. The change in momentum is equal to___.
A. power
B. impulse
C. work
D. force
4. A large truck and a small car are both driving the speed limit on the highway. The car has ___.
A. more momentum
B. less momentum
C. more acceleration
D. less acceleration
5. A man and a woman do the same amount of work. The woman does the job faster than the
man. The woman has more ___.
A. power
B. work (well duh, a woman’s work is never done!)
C. force
D. impulse
E. momentum
6. In order to have kinetic energy, an object must be___.
A. at rest
B. in an elevated position
C. moving
7. Which requires more work?
A. lifting a 50 kg sack vertically 2 m
B. lifting a 25 kg sack vertically 5 m
8. An object at rest may be said to have___.
A. impulse
B. work
C. power
D. kinetic energy
E. potential energy
9. A collision that causes deformation, generation of heat or both is an example of a(n)
_______inelastic_____ collision.
10. Energy can neither be ____created____ nor ___destroyed_____ according to the law of the
conservation of energy.
11. Increasing the time interval that a force is applied (decreases) (increases) the force.
12. Another term for (Newton)(meter) is __joule___.
13. Granny is roller skating and picks up her grandson Ambrose. Granny’s momentum before
picking up Ambrose is (greater than) (less than) (equal to) her momentum after picking up
Ambrose.
14. The __conservation____ of momentum states that the momentum before a collision is equal
to the momentum after a collision.
15. Colliding objects rebound without lasting deformation or the generation of heat. This is an
example of a(n) ___elastic____ collision.
16. Small changes in _velocity___ create large changes in _kinetic__energy_.
17. A 10 kg medicine ball is thrown at 30 m/s. What is the momentum of the medicine ball?
Momentum = mv (10 kg) (30 m/s) = 300 kg * m/s = 3.0 x 10 2 kg * m/s
18. A car has a momentum of 4500 kg-m/s and is traveling at 15m/s. What is the mass of the car?
Momentum = mv 4500 kg-m/s = (mass) (15m/s) m = 300 kg = 3.0 x 10 2 kg
19. A block is pushed up a 15m frictionless surface with a force of 5N. How much work is done?
W = Fd (15 m) (5N) = 75 J = 7.5 x 10 2 J
20. A block is pushed up a 20m frictionless surface with a force of 4N. How much work is done?
W = Fd
(20 m) (4N) = 100 J = 1.0 x 10 2 J
21. A girl pushes a ball up a 40 m frictionless surface with a force of 10N, and it took 15s. How
much power did she use?
W = Fd
40 m 10 N = 400 J
P=W/t
400 J / (15s) = 26.66 J/s =
2.67 x 10 1 J/s
22. The height of a ramp is 35m. How much does a package weigh if 70J of work are needed to
slide it up the ramp?
W = Fd 70 = (35 m) F F = 2N
23. Using 100J of work, an elevator is raised from the ground to the second floor in 10s. How
much power does the elevator use?
P = W / t 1000 J / 10s = 100 J / s
24. Bronco Brown leaps from a high cliff, attached to a bungee cord. He reaches top speed in 6
seconds. The cliff is 700 m high. His mass is 100 kg. He reaches the bottom of his fall in
9 sec.
A. What is his PE before he jumps? PE = mgh = 6.86 x 10 5 J
B. What is his velocity after 6 sec.? v = gt = (9.8 m / s2) ( 4 sec) = 5. 88 x 10 1 m/s
C. What is his momentum after 6 sec.? Momentum = mv =
(100 kg)(5. 88 x 10 1 m/s) = 5, 880 kg * m/s = 5. 88 x 10 3 kg * m/s
D. Impulse during the 3 sec. interval of slowing down is __5. 88 x 10 3 Ns__.
Ft = ∆mv
E. What is the force on the bungee cord during the 3 sec. of slowing down?
Impulse = Ft 5. 88 x 10 3 Ns = F (3 sec) F = 1960 N = 1.96 x 10 3 N