Let l be the length of block immersed in liquid as shown in the figure. When the block is floating, ∴mg=Alρm If the block is given vertical displacement y then the effective restoring force is F=−[A(l+y)ρg−mg]=−[A(l+y)ρg−Alρg] =−Alρgy Restoring force =−[Alρg]y. As this F is directed towards equilibrium position of block, so if the block is left free, it will execute simple harmonic motion. Here inertia factor = mass of block =m Spring factor =Aρg ∴ Time period, T=2π√