Energy
Chapter 7
Bell Work
Answer all questions on the
Test review half sheet.
7.1 What is energy?
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Energy measures the ability for things to
change themselves or to cause change in
other things.
Some examples are changes in
temperature, speed, position, pressure, or
any other physical variable.
7.1 Units of energy
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Pushing a 1-kilogram object with a force
of one newton for a distance of one meter
uses one joule of energy.
 A joule (J) is the
S.I. unit of
measurement
for energy.
One joule is a pretty small amount of energy.
Energy is measured in:
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a. newtons.
b. joules.
c. kg/m2
d. kg•m/s2
Energy Conservation
• Energy cannot be created.
• Energy cannot be destroyed.
• Energy can be converted from
one form to another.
Kinetic Energy
• Energy of motion
• KE = ½
2
mv
What do we call energy of motion?
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A. thermal energy
B. kinetic energy
C. potential energy
D. work energy
If you double your speed, your
kinetic energy becomes:
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A. 2 times smaller.
B. 4 times smaller.
C. 2 times bigger.
D. 4 times bigger.
What happens to the kinetic energy
of an object if you double the mass?
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A. 2 times smaller.
B. 4 times smaller.
C. 2 times bigger.
D. 4 times bigger.
Work and Potential Energy
• The work done on the ball gives the ball
gravitational potential energy.
• Gravitational potential energy = mgh
Gravitational
Potential Energy
• Energy stored in an object due to its
position.
An object’s gravitational potential
energy is directly related to all of the
following EXCEPT
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A. Mass
B. Speed
C. Height
D. Gravity
Where does the ball have the most
Gravitational Potential Energy?
A.
B.
C.
D.
Where does the ball have the most
Kinetic Energy?
A.
B.
C.
D.
Bill lifts a 25-kg child from the ground
onto a 1.5 meter high table. What is the
potential energy of the child?
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A. 37.5 J
B. 16.67 J
C. 367.5 J
D. None! A child never has potential
energy.
How high would you need to lift a 5-kg
box to increase its potential energy by
1000 joules?
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A. about 5000 m
B. about 500 m
C. about 200 m
D. about 20 m
Elastic
Potential Energy
• Energy stored in an object due to its
shape.
• The work done changing the shape of
an object is stored elastic potential
energy.
A stretched rubber band has
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A. elastic potential energy.
B. Mechanical potential energy.
C. Chemical potential energy.
D. None of these
A wind-up toy has
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A. elastic potential energy.
B. Mechanical potential energy.
C. Chemical potential energy.
D. None of these
A compressed basketball has
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A. elastic potential energy.
B. Mechanical potential energy.
C. Chemical potential energy.
D. None of these
Energy cannot be created or destroyed.
Energy can be converted from one form
to another. Is an example of
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A. Newton’s first law
B. The law of conservation of energy
C. The pendulum law
D. None of these
• Where does the pendulum have the
most Pe? A B C D E
• Where does the pendulum have the
most Ke? A B C D E
Both Ball #1 and Ball #2 rolls down the
hill. Ball #1 goes on the steeper side.
Compare the speed at the bottom.
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a. Ball #1 has the greater speed.
b. Ball #2 has the greater speed.
c. The speed will be the same for both balls.
d. Not enough information is given.
A 2 Kg ball is released from rest at the top of a
track and reaches a speed of 10 m/s at the
bottom.
a. How much kinetic energy does the ball have?
b. How much potential energy does it have at the top of the hill
(assuming no energy was lost)?
c. What was the height of the hill?
A 3 kg rock sits on a 0.8 meter ledge. If it is pushed
off, how fast will it be going at the bottom?
A 4 kg ball is on a 5 m ledge. If it is
pushed off the ledge, how much kinetic
energy will it have just before hitting the
ground?
How high up is a 3 kg object that has
300 joules of energy?
A rolling ball has 18 joules of kinetic
energy and is rolling 3 m/s. Find its mass.
A 4 kg bird has 8 joules of kinetic
energy. How fast is it flying?
Match the Units
1. F or Fw = ________
2. v = ______________
3. h = ______________
4. W or E= __________
5. P = ______________
8
8
8
8
8
w
N
m
J
m/s