# Homework Help: Rotational Inertia of a door

1. Nov 13, 2005

### Nm

A rotating door is made from four rectangular glass panes, as shown in the drawing. The mass of each pane is 76 kg. A person pushes on the outer edge of one pane with a force of F = 55 N that is directed perpendicular to the pane.

a.) Find the rotational inertia of the door.
b.) Find the magnitude of the door's angular acceleration.
c.) Find the time it would take to rotate the door a half-circle (assuming it started from rest.)
I have tried calculating the torque for the pane to be (1.2m)(55N) = 66 Nm. I think the rotational inertia should be I = 1/3ML^2 multiplied by 4 for each pane since it is spinning away from the center of mass (edge). Can someone tell me if this is correct? I don't know how to continue this problem...Thanks.

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2. Nov 13, 2005

### Nm

I figured out the solutions so never mind.

3. Nov 14, 2005

### skinnyabbey

I thought torque was rotational inertia multiplied by acceleration(in radians). You found your torque by multiplying the distance by the force? Can you exlplain your steps bcz I have a test on Friday on Rotation, and this could be very useful