e.
a unit of energy
41. An object moving in a circle at a steady speed has
a.
constant linear momentum
b.
constant angular momentum
c.
constant velocity
d.
constant acceleration
42. His kinetic energy at the top of the hill is
a.
0 J
c.
some value between 0 and 500 J
b.
500 J
d.
none of the above
43. He slides part way down the hill to a point where his gravitational potential energy is 200 J.
His kinetic energy at that point will be
a.
200 J
b.
300 J
c.
some unknown value between 0 and 500 J
d.
none of the above
44. He slides all the way down to the valley bottom where his gravitational potential energy
becomes zero. His kinetic energy at the bottom will be
a.
0 J
c.
some value between 0 and 500 J
b.
500 J
d.
none of the above
45. Suppose after reaching the bottom he then continues sliding up another icy slope on the
other side of the valley. When he finally comes to a stop he will have reached a height
a.
equal to the height he started from on the other hill
b.
less than the height he started from on the other hill
c.
more than the height he started from on the other hill
d.
none of the above
46. The mass of 1 m3 of fresh water is 1,000 kg. At the top of a hydroelectric dam the potential
energy of the water is:
a.
1,000 N
b.
9,800 N
c.
500 N
d.
There is not enough information to calculate the potential energy
47. The mass of 1 cubic meter of fresh water is 1,000 kg. At the top of a 100 m hydroelectric
dam the potential energy of the cubic meter of water is:
a.
10,000 N
c.
100,000 N
b.
98,000 N
d.
980,000 N
48. The mass of 1 cubic meter of fresh water at the top of a 100 m hydroelectric dam is 1,000 kg
and it has a potential energy of 980,000 N. At the bottom of the dam, the speed of the
moving water is:
a.
9,800 m/s
c.
44.3 m/s
b.
1,960 m/s
d.
98 m/s
49. A mechanic working on a 100 m radar tower drops a hammer weighing 44.5 N. The work
done on the hammer as it falls is:
a.
4.45 N-m
c.
445 N-m
b.
44.5 N-m
d.
4,450 N-m
MULTIPLE RESPONSE
1. Linear momentum is conserved in
a.
an inelastic collision
b.
an elastic collision
c.
any collision where two objects rebound off each other
d.
none of the above
2. The total kinetic plus potential energy of a body
a.
can be negative
b.
always stays constant if the body is freely falling
c.
always stays constant if friction is acting
d.
can remain constant even if the body’s speed is decreasing
3. A barbell is easier to twist when its weights are
a.
close to the axis of rotation
b.
near the ends of the bar
c.
heavy
d.
light
e.
none of the above
4. After the dropped box hits the floor, its kinetic energy is
a.
0
b.
equal to its potential energy
c.
is converted to internal energy
d.
none of the above
5. The 1 cubic meter of fresh water at the top of a 100 m hydroelectric dam has a potential
energy of 980,000 N. At the bottom of the dam,
a.
The kinetic energy is 980,000 N
b.
All of the kinetic energy can be converted to electricity
c.
Some of the kinetic energy is converted to electricity and some is lost.
d.
The residual potential energy of the water is 9,800 N
COMPLETION
1. In a collision the total ____________ is the same before and after.
2. To be able to do work, a system must have _______.
3. An object has kinetic energy when it is __________.
4. Kinetic energy is conserved in __________ collisions.
5. Linear momentum is conserved in __________ collisions.
6. The energy stored in a pile driver is an example of __________ energy.
7. The energy stored in a stretched spring is an example of __________ energy.
8. The energy of a body moving across a horizontal surface is an example of __________
energy.
9. The energy in the water at the top of a waterfall is an example of __________ energy.
10. As a skier gains speed skiing down a slope, ______ energy is being converted to _________
energy.
11. Angular momentum __________ conserved.
12. Linear momentum __________ conserved.
13. Kinetic energy __________ conserved.
14. The kinetic energy of the crate is __________.
15. The potential energy of the crate is __________.
16. The linear momentum of the crate is __________.
17. The work you do on the crate is __________.
18. The power you supply to the crate is __________.
19. You carry a 20 N box 5 m horizontally across a room. The work you do is __________.
20. The work you do is __________.
21. The increase of potential energy of the box is __________.
22. You drop the box. As it falls to its original level, its kinetic energy is __________.
23. After you drop the box and it has fallen half way, its potential energy is __________ and its
kinetic energy is __________.
24. After the dropped box hits the floor, its kinetic energy is converted into ____________.
25. A 2 kg car moving towards the right at 4 m/s collides head on with an 8 kg car moving
towards the left at 2 m/s, and they stick together. After the collision, the velocity of the
combined bodies is __________ m/s pointing __________.
26. A person runs up a long flight of stairs in 10 seconds. If the person’s weight is 600 N and
the vertical height of the stairs is 20 meters, the person’s power output is __________.
27. In a collision that is inelastic, the total _________ after the collision is not the same as
before the collision.
28. A worker on top of a radar tower 80 m high drops a wrench off the tower. The speed of the
wrench when it hits the ground is ____________
29. A hunter notches a 0.05 kg arrow in a compound bow and draws the arrow back to set the
bow. The hunter does 50 J of work in the process setting the bow/arrow combination and
then releases the arrow. The speed of the arrow is ___________.
30. A light aircraft that weighs 1,600 N is accelerated at 8 m/s/s for 15 seconds. The work done
on the aircraft is _________.
MATCHING
Match each item with the correct statement below.
a.
angular momentum
h.
kinetic energy
b.
elastic collision
i.
lever
c.
elastic potential energy
j.
linear momentum
d.
energy
k.
power
e.
gravitational potential energy
l.
work
f.
heat
m.
internal energy
g.
inelastic collision
1. type of collision in which kinetic energy is conserved
2. the rate of doing work
3. associated with circular motion
4. can be stored in a spring
5. energy due to motion
6. type of collision in which kinetic energy is not conserved
7. the mass of an object times its velocity
8. the measure of a system’s capacity to do work
9. the energy source for a hydroelectric power station
10. the force that acts times the distance moved in the direction of the force
11. The type of energy contained in a compound bow when drawn to its maximum extension.
PROBLEM
1. A 50 kg ice skater moving at 6 m/s collides with a second stationary skater with mass 70 kg.
The skaters cling together after the collision and move without friction. Compute their speed
after the collision.
2. A railroad car with a mass of 20,000 kg rolls into a second stationary car with a mass of
40,000 kg. The cars latch together and move off with a speed of 1.2 m/s. How fast was the
first car moving before the collision?
3. A mover slides a refrigerator 5 meters across a floor. If a force of 200 N was used, how
much work was done?
4. A person with a mass of 60 kg climbs up to a diving board 4 meters above a swimming
pool.
(a) How much work does the person do?
(b) What is the diver’s kinetic energy upon entering the water after diving off?
5. What is the kinetic energy of a 5,000 kg truck traveling at 25 m/s?
6. A bicyclist starts from rest at the top of a hill and rolls down the hill without pedaling.
Assuming there is no friction and the bottom of the hill is 20 meters below the top, what is
the bicyclist’s speed at the bottom of the hill?
7. A ball is thrown straight upward with an initial speed of 30 m/s. Assuming there is no air
resistance, how high does the ball go before falling back down?
8. A person runs up a long flight of stairs in 10 seconds. If the person’s weight is 600 N and
the vertical height of the stairs is 20 meters, what is the person’s power output?
9. A 15,000 watt motor is used to lift a 18,000 kg aircraft to a height of 10 m. How much time
does it take to lift the aircraft with the motor?