11 Energy and Its Conservation
BIGIDEA
Write the Big Idea for this chapter.
Use the “What I Know” column to list the things you know about the Big Idea. Then list the
questions you have about the Big Idea in the “What I Want to Find Out” column. As you read the
chapter, fill in the “What I Learned” column.
W
What I Want to Find Out
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K
What I Know
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L
What I Learned
11 Energy and Its Conservation
1 The Many Forms of Energy
MAINIDEA
Write the Main Idea for this section.
REVIEW VOCABULARY
Recall and write the definition of the Review Vocabulary term.
system
system
NEW VOCABULARY
Use your book to fill in the term that matches each definition.
energy due to rotational motion
energy stored due to interactions between objects in a system
stored energy due to the gravitational force between objects
position where GPE is defined to be zero
the sum of the kinetic energy and potential energy of the particles in a
system
Student Edition, pp. 292–293
Identify two ways work can change the kinetic energy of an object.
Science Notebook • Energy and Its Conservation
164
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stored energy due to an object’s change in shape
1 The Many Forms of Energy (continued)
Student Edition, pp. 292–297
Differentiate When should Wg = mgh have a negative sign?
Describe the work done by gravity as the orange rises from
the juggler’s hand.
GET IT?
Explain why it is important to specify a reference level before you
calculate the gravitational potential energy of an object.
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Use with Example Problem 1.
Use this column for
scratch work and
sketches.
TRY IT !
Problem
GRAVITATIONAL POTENTIAL ENERGY You lift a 6.5-kg backpack from a
chair that is 0.47 m above the floor (hc) to a desk that is 0.75 m above the
floor (hd)
a. When the backpack is on the desk, what is the backpack-Earth
system’s gravitational potential energy relative to the floor (GPE1)?
b. When the backpack is on the desk, what is the backpack-Earth
system’s gravitational potential energy relative to the chair (GPE2)?
c. How much work was done by gravity as you lifted the backpack
from the chair to the desk?
1. ANALYZE AND SKETCH THE PROBLEM
KNOWNS
UNKNOWNS
m=
g=
=?
hd =
hc =
=?
Science Notebook • Energy and Its Conservation
165
=?
1 The Many Forms of Energy (continued)
Student Edition, pp. 297–300
TRY IT ! (continued)
2. SOLVE FOR THE UNKNOWNS
a. Set the floor as the reference level. Determine GPE1.
b. Set the chair as the reference level. Determine GPE2.
First determine the height of the desk relative to the chair.
Next use this difference in height to determine GPE2.
c. Calculate work by multiplying the weight of the backpack times
the distance it was lifted. The direction of weight is opposite
that of h.
• Explain why the two values of GPE are reasonable.
GET IT?
Define the term elastic potential energy.
Decide A student states that thermal energy is the sum of an object’s
kinetic energy and potential energy. What is wrong with the statement?
Science Notebook • Energy and Its Conservation
166
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3. EVALUATE THE ANSWER
1 The Many Forms of Energy (continued)
SUMMARIZE
How does the MAINIDEA for this section relate to the chapter’s BIGIDEA?
REVIEW IT !
11. MAINIDEA How can you apply the work-energy theorem to lifting a bowling ball
from a storage rack to your shoulder?
12. Elastic Potential Energy You get a spring-loaded jumping toy ready by compressing
the spring. The toy then flies straight up. Draw bar graphs that describe the forms of
energy present in the following instances. Assume the system includes the spring toy
and Earth.
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a. The toy is pushed down, thereby
compressing the spring.
b. The spring expands and the toy
jumps.
c. The toy reaches the top of its flight.
Science Notebook • Energy and Its Conservation
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1 The Many Forms of Energy (continued)
12. Potential Energy A 25.0-kg shell is shot from a cannon at Earth’s surface. The reference
level is Earth’s surface.
a. What is the shell-Earth system’s gravitational potential energy when the shell’s
height is 425 m?
b. What is the change in the system’s potential energy when the shell falls to a height
of 225 m?
13. Potential Energy A 90.0 kg rock climber climbs 45.0 m upward, then descends 85.0 m.
The initial height is the reference level. Find the potential energy of the climber-Earth
system at the top and at the bottom. Draw bar graphs for both situations.
Science Notebook • Energy and Its Conservation
168
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14. Rotational Kinetic Energy On a playground, some children push a merry-go-round so
that it turns twice as fast as it did before they pushed it. What are the relative changes
in angular momentum and rotational kinetic energy of the merry-go-round?
1 The Many Forms of Energy (continued)
15. Critical Thinking Karl uses an air hose to exert a constant horizontal force on a puck,
which is on a frictionless air table. The force is constant as the puck moves a fixed
distance.
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a. Explain what happens in terms of work and energy. Draw bar graphs.
b.
Suppose Karl uses a different puck with half the first one’s mass. All other
conditions remain the same. How should the kinetic energy and work done differ
from those in the first situation?
c.
Describe what happened in parts a and b in terms of impulse and momentum.
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