Physics: Rotating Door problem?

Question

A rotating door is made from four rectangular glass panes, as shown in the drawing. The mass of each pane is 82 kg. A person pushes on the outer edge of one pane with a force of F = 76 N that is directed perpendicular to the pane. Determine the magnitude of the door's angular acceleration.
________rad/s^2

http://www.webassign.net/CJ/09_34.gif

Answer 1

Moment of inertia of each pane of the door = mr^2/3
Total moment of inertia of the door I = 4mr^2/3
Torque T = Fr
Ang. accel = I*T