Answer:
i. The rock can be referred to as the bob.
ii. The point at which the string was held can be referred to as the pivot.
iii. The length of the string from its point of suspension to the rock is the given length of the pendulum.
Explanation:
A pendulum is a weight suspended from a pivot so that it can freely perform an oscillatory motion. It consists of majorly three parts: bob, pivot and length. Its motion deals with the conversion of kinetic energy to potential energy, and vice versa. When set in motion, at the extreme ends of its oscillation, it has maximum potential energy. But when at the mid-point of the curve path, it has maximum kinetic energy.
Some of its properties can be used to describe other objects.
For the given pendulum, the rock represents the bob, the point at which the string was held is the pivot, and the length of the string fom pivot to bob is the length of the pendulum.