A  m$=2\mathrm{.}21$ kg mass is attached to a thin uniform rod of mass M rod $=4\mathrm{.}79$ kg and length L $=89$ cm is pivoted at point O and initially held in the horizontal position .The rotational inertia of the rod about the center of mass is I cm $=1/12$ML$\mathrm{²}.($Take g $=9\mathrm{.}8$ m$/$s$\mathrm{²}).$ What is the angular acceleration of the rod just it is released from rest?