# Homework Help: Rotational dynamics-rotating door w/ 4 panes

1. Dec 1, 2007

### Kate Green

1. The problem statement, all variables and given/known data

A rotating door is made from four rectangular glass panes, as shown in the drawing. The mass of each pane is 90 kg. A person pushes on the outer edge of one pane with a force of F = 80 N that is directed perpendicular to the pane. Determine the magnitude of the door's angular acceleration.________rad/sec squared. (there is a pic that shows radius 1.2m)

2. Relevant equations
net external torque=moment of inertia x angular acceleration

3. The attempt at a solution
Tried (90kg*4 panes*1.2m squared) to get moment of inertia=518.40. Then divided 80N b
by 518.40 to solve for angular accel=.1543 This isn't right. Will anyone help?

2. Dec 1, 2007

### OJones

So the force of 80N is applied at 1.2m from the axis of rotation, correct? For your calculation of Torque/m.o.i., you have used T=80N. Numerically, are you sure about that? Dimensionally, are you sure about that? Look again...

3. Dec 1, 2007

### FedEx

$$\tau\ = I\alpha}$$

You have placed force instead of torque in the above equation.

4. Dec 1, 2007