A cylindrical block of wood (density $= 650 \;kg\;m^{-3} )$, of base area $30\;cm^2$ and height $54\;cm$ , floats in a liquid of density $900\;kg\;m^{-3}$. The block is depressed slightly and then released . The time period of the resulting oscillations of the block would be equal to that of a simple pendulum of length (nearly)