PHYSICS 112  SPRING 2003  EXAM 1  February 12, 2003
Name: _____________________________________
Recitation Section Number: ______
SHOW YOUR WORK!
Although some of these problems are multiplechoice, full credit
will be given only if you explain how you arrived at your answer.
Either show your work
(especially in a calculation) or give a short explanation.
Nothing elaborate is required.
1.
(6 points)
Two electric charges are 3 m apart.
Suppose that the forces that they exert on
each other have magnitude 12 N, and that their electrical potential energy is
36 J.
What
will be the corresponding quantities if they are moved to a separation of 6 m?
Magnitude of forces at 6 m separation:
Electrical potential energy at 6 m separation:
2.
(6 points)
The diagram shows the electric field at the origin.
Indicate on the diagram by
a point labeled N where a single negative electric charge might be located if it (by itself)
produces this electric field.
Indicate on the diagram by P
and P
where two identical
1
2
positive charges might be located on the axes if they together produce this electric field.
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3.
(6 points)
A charge Q
is fixed at the origin and another charge Q
is located 2 m away.
1
2
Charge Q
is at rest, and the electrical potential energy of the system is 12 J.
If charge
2
Q
moves away from the origin, what will be its kinetic energy when it is 4 m away from the
2
origin?
0 J
2 J
4 J
6 J
8 J
10 J
12 J
16 J
24 J
The following diagram is to be used with the rest of the problems on this exam.
It shows a
positive electric charge of
2 C at the origin and a
5C charge located at
3 m on
C œ
the positive
axis.
C
4.
(6 points) On the diagram, draw vectors showing the forces on the two charges, making
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 Summer '08
 Fretwell
 Work, Electrical Potential Energy, Electric charge

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