# Moment of Inertia and Angular Speed

1. Oct 27, 2006

### TrippingBilly

A top has a moment of inertia of 4.40 10-4 kgm2 and is initially at rest. It is free to rotate about the stationary axis AA'. A string, wrapped around a peg along the axis of the top, is pulled in such a manner as to maintain a constant tension of 5.19 N. If the string does not slip while it is unwound from the peg, what is the angular speed of the top after 80.0 cm of string has been pulled off the peg? (The picture of the top shows it rotating clockwise about a vertical axis A)

This question has me stumped. If someone could point me in the right direction with regards to a concept I need to know or something I would appreciate it.

2. Oct 27, 2006

### Staff: Mentor

Hint: How much work is done by the string?

3. Nov 2, 2006

### TrippingBilly

At first I didn't see where you were going, but then I realized that work = change in energy. Which enabled me to use that wonderful equation
delta K = .5I(final angular velocity^2 - initial angular velocity^2). Thanks for the hint!