Which statement about electric force is true?
a) it is a purely attractive force.
b) it is a purely repulsive force.
c) it is both an attractive and a repulsive force.
d) it is neither an attractive nor a repulsive force.

the motion of a pendulum is a classic example of mechanical energy conservation. a pendulum consists of a mass (known as a bob ) attached by a string to a pivot point. as the pendulum moves it sweeps out a circular arc, moving back and forth in a periodic fashion.