# Homework Help: Rotational Dynamics Problem

1. Nov 28, 2007

### PhysicsZax

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

Two thin rectangular sheets (0.20 m x 0.43 m) are identical. In the first sheet the axis of rotation lies along the 0.20-m side, and in the second it lies along the 0.43-m side. The same torque is applied to each sheet. The first sheet, starting from rest, reaches its final angular velocity in 8.8 s. How long does it take for the second sheet, starting from rest, to reach the same angular velocity?

2. Relevant equations

T = Iw/t

3. The attempt at a solution

The moment of inertia for a sheet of paper, I = 1/3mL^2

((0.43)^2 * 1/3) / 8.8 s = ((0.2)^2 * 1/3) / t

t = 1.9 s

This doesn't appear to be the correct answer. Any ideas? Do I have the Lengths backwards? Any help would be much appreciated!

Thanks!

Zach

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