Ans.

If L be the distance between the centre of suspension and centre of oscillation of the compound pendulum then the time period of oscillation of the compound pendulum is

\( \displaystyle{T=2\pi\sqrt{\frac{L}{g}}} \)

where, \( g \) is the acceleration due to gravity.

For a second pendulum the time period of oscillation is 2 sec.

therefore, \( \displaystyle{2=2\pi\sqrt{\frac{L}{g}}} \)

or, \( \displaystyle{L=\frac{g}{{\pi}^2}} \)

or, \( L=\frac{980}{3.14} \) cm

or, \( L=99.19 \) cm