Question

a simple pendulum is hollow from within and its time period is T. how is the time period of pendulum affected when:
a) ¼ of Bob is filled with mercury
b)¾ of Bob is filled with Mercury
c) the bob is completely filled with Mercury
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Answer 1

The period of a pendulum is independent of the mass of the bob so whether it's empty or filled with something, the period remains the same.

$period = 2\pi \sqrt{ \frac{length}{g} }$