Conceptual Physics Chapter 8: Energy
+
+ +
_____________________________________________
2.28
PART I Problems (80)
Solve these problems on your own paper.
Solve each problem on its own page, do not put more
than one problem on a page! You must use the Three-Column-Method to receive any
credit for your work.
1. Consider 100 kg of bricks.
a) How much do these bricks weigh?
b) How much work is done to lift these bricks 5 m?
c) How much gravitational potential energy do the bricks have
after being lifted?
2. A 60 kg student runs at 2.0 m/s.
a) How much kinetic energy does the student have?
b) Answer this question in a complete sentence and explain how you
know: If the student now runs 6 m/s by how much does his kinetic energy
increase?
c) How much work does the student do in order to increase his
velocity?
d) If the student takes 5 seconds to change his speed how much
power did he exert?
e) The student’s acceleration was 0.8 m/s2. How many
meters did he run by the time he reached a velocity of 6 m/s?
PART II: Short Answer (60)
Answer the questions below on your own
paper. Put each question on its own page, do not put
more than one question on a page. Answer each question in ‘a’, ‘b’, ‘c’ bullet
format.
3. Consider gravitational potential energy:
a) If a rubber ball that has 300 J of gravitational potential
energy is dropped by what law of the universe do we know it will have 300 J of
kinetic energy just before it hits the floor?
b) State the law cited
in part ‘a’.
c) By the Law referred to in part ‘a’ the ball should bounce to
its original height but it never does. According to the Law the energy cannot
disappear. What happened to the energy of the ball such that it could not
bounce to its original height?
4. Consider kinetic energy:
a) How can you tell whether an object has kinetic energy or not?
b) An object has 300 J of kinetic energy; if it maintains its
velocity but loses two thirds of its mass what will its kinetic energy be?
c) An object has 300 J of kinetic energy, if its mass remains
constant but is velocity increases by a factor of 3 what will its kinetic
energy be?
PART III True/False (30)
Indicate whether the statement is true
or false. Mark your answer document ‘A’ for true and ‘B’ for false.
PART IV Rewrite (60)
On your own paper rewrite the false
statements so that they will be true. Be sure to address all of the areas of
the false statement that are false. You will receive ten (10, 5+5, X) points
for each correctly rewritten statement. Do NOT copy the false statements nor is
it necessary to rewrite the true statements.
5. In physics the amount of work done on an
object is the product of the force applied to the object and the time during
which that force is applied.
6. Whenever gravitational potential energy, mgh, is converted into kinetic energy, 
,
only half of the total energy is actually converted.
7. Power is the rate at which work is done.
8. Because it takes longer to walk up a flight
of stairs than
it does to run up the same stairs, more power is exerted when you walk up the
stairs.
9. The energy an object has because it is moving
is called kinetic energy.
10. The SI unit for work is the Watt; the SI unit
for power is the Joule; the SI unit for energy is the N/m.
11. When an object is carried, rather than pushed,
across a room no work is done on the object because the force is perpendicular
to the direction of motion.
12. Whenever work is done a force must be applied and
there must be motion in the direction of the force.
13. If car ‘A’ skids 90 m and car ‘B’, of the same
mass, skids only 10 m car ‘b was going nine times slower than car ‘A’
14. According to the law of conservation of energy,
energy can be created but it can never be destroyed.
PART V: Multiple Choice
(33)
Identify the choice that best completes
the statement or answers the question.Carefully place
your answer choice on your answer document.
15. Which of these is the SI unit for work?
|
a. |
Watt |
c. |
Newton per meter |
|
b. |
Joule |
d. |
Joule per second |
16. The kinetic energy of an object is a function
of the object’s
|
a. |
force and mass. |
c. |
mass and velocity. |
|
b. |
weight and velocity. |
d. |
force and power. |
17. The potential energy of an object is a function
of an object’s
|
a. |
mass and velocity. |
c. |
weight and acceleration |
|
b. |
velocity and height. |
d. |
weight and height. |
18. A job is done slowly, while an identical job is
done quickly. Both jobs require the same amount of work.but
different amounts of
|
a. |
power. |
c. |
kinetic energy. |
|
b. |
force. |
d. |
potential energy. |
19. A ball is thrown into the air with an initial
100 J of kinetic energy. At the top of its path it has
|
a. |
50 J of kinetic energy and 50 J of
gravitational potential energy. |
c. |
0 joules of gravitational potential
energy and 0 Joules of kinetic energy. |
|
b. |
0 Joules of gravitational potential
energy and 100 Joules of kinetic energy. |
d. |
0 Joules of kinetic energy and 100 J
of gravitational potential energy. |
20. A one kilogram object moving at one meter per
second has a kinetic energy of
|
a. |
0.5 J |
c. |
5 J |
|
b. |
1.0 J |
d. |
10 J |
21. The SI unit for power is
|
a. |
the Joule-second |
c. |
the Newton -meter |
|
b. |
a Watt |
d. |
a Joule |
22. Power is
|
a. |
the ability to do
work. |
c. |
impulse times time. |
|
b. |
the rate at which work
is done. |
d. |
energy in motion. |
23. An Earth satellite in elliptical orbit is going
|
a. |
fastest when it is nearest
Earth. |
c. |
slowest when it is nearest
Earth. |
|
b. |
fastest when it is
farthest from Earth. |
d. |
the same speed all the
time. |
24. All of the energy of a car comes from
|
a. |
the kinetic energy of
the car’s motion. |
c. |
the energy stored in
the gasoline. |
|
b. |
the energy stored in
the car’s battery. |
d. |
the energy stored in
the car’s engine. |
25. A ball never bounces to its original height
because
|
a. |
some of its kinetic
energy simply goes away. |
c. |
energy is created when
the ball bounces. |
|
b. |
some of its potential
energy is not fully converted into other kinds of energy. |
d. |
some of the kinetic
energy is converted into sound and heat. |
