A hollow cylinder of mass m made heavy at its bottom is floating vertically in water. It is tilted from its vertical position through an angle and is left. The restoring force acting on it is
l = length of cylinder
A = Area of crossection of cylinder
mg = (A) (l) (ρ) (g)
m = Alρ
When cylinder is tilted through an angle
length of cylinder in water = 1cos θ
wt of water displaced = lcos θA ρ g
restoring force = lAρgcos θ−lAρg
= lAρg(1cos θ−1)=mg(1cos θ−1)