8B Worksheet Answers
1. Charge and Coulomb’s Law
1. a) Both balls will experience the
same
magnitude of force [Newton’s third law still
applies!]
b) The balls are identical, and therefore have the same mass. By
F
=
ma
, since they
experience the same force, they experience the same acceleration.
c) Ball A initially feels a force to the left, and will accelerate to the left. As ball A moves
away from ball B, the force that it feels will
decrease
, since the distance separating
the charge
increases
. The acceleration will therefore always be to the left and have a
magnitude which will decrease down to zero when the balls are infinitely far apart.
d) Ball A starts with zero velocity, but the non-zero acceleration gives it a velocity to the
left. As time goes on, the velocity increases, but at a slower and slower rate [the
acceleration is decreasing]. As the acceleration drops to zero, the ball will reach a
maximum velocity [after an infinite amount of time, when the balls are ‘infinitely’ far
apart].
e) We want ball C to provide a force to counter ball B’s. Since the force acts to the left,
we want the force by C on A to be to the right. A and C have the same sign of charge
and will repel. Therefore, you need to place Ball C to the
left
of A.
f) Ball C should be a distance

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