Question

The bob of a simple pendulum is a hollow sphere filled with
water. How does the period of oscillation change if the water
begins to drain out of the sphere?

Answer 1

The time period first increases then decreases .As water starts draining out, Centre of Mass of system starts shifting down, hence increasing the effective length. As a certain amount of water drains the COM of system again starts shifting back to its orginal position, thus decreasing the effective length. Hence the time period first increases then decreases .

Answer 2

the water inside the bob start to leak and due to this leakage the mass of the bob reduces and due to which the movement of the bob increases