A non uniform cylinder of mass `m`, length `l` and radius `r` having its C.O.M at a distance `(l)/(4)` from centre and lying on axis of cylinder . The cylinder is kept in a liquid of unifrom density `rho`. The moment of inertia of the rod about C.O.M is I. The angular acceleration of point A relative to point B just after the rod is released from position shown in figure is .