Question

A simple pendulum is made of a bob which is a hollow sphere containing mercury, suspended by a means of a wire. If mercury is drained off continuously the period of the pendulum will

A) remain unchanged.

B) first increase, then decrease

C) decreases.

D) become erratic

and Why?

Answer 1

Answer: B. first increase, then decrease

Reason:

The draining of mercury from the bob started it will shift the center of mass of the whole system downwards. This will increase the length of the oscillating system and thus the time period will increase.
After draining mercury fully the centre of mass regains its position to the centre of bob. Thus the length of centre of mass decreases.so that the time period will decreases .

So option B is the correct answer.