The bob of a simple pendulum is a hollow cylinder, with a small hole in the bottom. It is filled with sand and set into oscillation. Its periodic time (T) is measured at regular intervals. As the sand starts coming out we find that

Options

A. T increases with time
B. T does not change with time
C. T first decrases and then increases
D. T first increases and then decreases

Answer

D

Explanation

As more and more sand particles come out, the centre of mass is shifted downwards and the effective length of the simple pendulum increases and as `T prop L` period increases. But afterwards it is shifted upwards and hence L decreases and T increases.