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MasteringPhysics: Assignment Print View
Introduction to Potential Energy
Learning Goal:
Understand that conservative forces can be removed from the work integral by
incorporating them into a new form of energy called potential energy that must be added to the
kinetic energy to get the total mechanical energy.
The first part of this problem contains shortanswer questions that review the workenergy theorem.
In the second part we introduce the concept of potential energy. But for now, please answer in terms
of the workenergy theorem.
WorkEnergy Theorem
The workenergy theorem states
,
where
is the work done by
all
forces that act on the object, and
and
are the initial and
final kinetic energies, respectively.
Part A
The workenergy theorem states that a force acting on a particle as it moves over a ______
changes the ______ energy of the particle.
Choose the best answer to fill in the blanks above:
ANSWER:
distance / potential
distance / kinetic
vertical displacement / potential
none of the above
Part B
To calculate the change in energy, you must know the force as a function of _______. The work
done by the force causes the energy change.
Choose the best answer to fill in the blank above:
ANSWER:
acceleration
work
distance
potential energy
Part C
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To illustrate the workenergy concept, consider the case of a stone falling from
to
under the
influence of gravity.
Using the workenergy concept, we say that work is done by the gravitational _____, resulting in
an increase of the ______ energy of the stone.
Choose the best answer to fill in the blanks above:
ANSWER:
force / kinetic
potential energy / potential
force / potential
potential energy / kinetic
Potential Energy
You should read about potential energy in your text before answering the
following questions.
Potential energy
is a concept that builds on the workenergy theorem, enlarging the concept of
energy in the most physically useful way. The key aspect that allows for potential energy is the
existence of conservative forces, forces for which the work done on an object does not depend on
the path of the object, only the initial and final positions of the object. The gravitational force is
conservative; the frictional force is not.
The change in potential energy is the
negative
of the work done by conservative forces. Hence
considering the initial and final potential energies is equivalent to calculating the work done by the
conservative forces. When potential energy is used, it
replaces the work
done by the associated
conservative force. Then only the work due to
nonconservative
forces needs to be calculated.
In summary, when using the concept of potential energy, only
nonconservative
forces contribute to
the work, which now changes the total energy:
,
where
and
are the final and initial potential energies, and
is the work due
only
to
nonconservative forces.
Now, we will revisit the falling stone example using the concept of potential energy.
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This note was uploaded on 10/12/2010 for the course PHYS 4A taught by Professor Ernest during the Spring '10 term at Irvine Valley College.
 Spring '10
 Ernest
 Energy, Force, Potential Energy, Work

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