text: physics question below? a rotating door is made from four rectangular glass panes, the width of each rectangular glass pane is 1.2 m. the mass of each pane is 78 kg. a person pushes on the outer edge of one pane with a force of f = 66 n that is directed perpendicular to the pane. determine the magnitude of the door's angular acceleration. treat this problem as a point source of mass on a massless arm. mass (m) = 4 * 78 kg = 312 kg arm length (radius, r) = 1.2 m force (f) = 66 n  moment of inertia = m*r^2 (kg-m^2) = 312 * 1.2 * 1.2 = 449.28 kg-m^2  from wikipedia; http://en.wikipedia.org/wiki/moment_of_inertia: "the (scalar) moment of inertia of a point mass rotating about a known axis is defined by     i = m * r^2 where,     m is its mass,     and r is its perpendicular distance from the axis of rotation."  angular acceleration (α)= τ/i = (f * m)/i = (66 * 1.2)/ 449.28 = 0.176 rad/sec^2  from wikipedia; http://en.wikipedia.org/wiki/angular_acceleration "   α = τ/i (rad/sec^2) where,    τ is torque    i is moment of inertia. "  hope this helps!