The revolving door consists of four doors which are attached to an axle AB. Each door ca...

The revolving door consists of four doors which are attached to an axle AB. Each door can be assumed to be a 50-lb thin plate. Friction at the axle contributes a moment of 2 lb • ft which resists the rotation of the doors. If a woman passes through one door by always pushing with a force P = 15 lb perpendicular to the plane of the door as shown, determine the door's angular velocity after it has rotated 90°. The doors are originally at rest.