A revolving door has four panels, equally spaced. From rest four people push the

Question

A revolving door has four panels, equally spaced. From rest four people push the door on their respective panel. Each person pushes perpendicular to the panel. Person #1 pushes on panel #1 in a clockwise motion 1 mm from the axis of rotation with a force of 10000 N; Person #2 pushes on panel #2 in a counterclockwise motion 10 mm from the axis of rotation with a force of 1000 N; Person #3 pushes on panel #3 in a clockwise motion 100 mm from the axis of rotation with a force of 100 N; Person #4 pushes on panel #4 in a counterclockwise motion 1000 mm from the axis of rotation with a force of 10 N; What is the net torque? What is the angular acceleration?

Explanation / Answer

torque=force*peripendicular distance of the force from the axis of rotation

assume that clockwise torque be +ve and anti-clockwise torque to be -ve.

then total torque=10000*0.001-1000*10*0.001+100*0.10-10*1=0 N.m

part a:

hence total torque is 0 N.m

part b:

as torque=angular acceleration*moment of inertia

and torque in the given situation is 0 N.m, angular acceleration is 0 rad/s^2.

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