# Homework Help: Newton's Second Law of Rotation

1. Oct 28, 2007

### Momentum09

1. The problem statement, all variables and given/known data
We have a rigid bar (length L) with an axis of rotation through the center of the bar. The bar is attached to a pulley with radius Rp at the axis of rotation. Two lead weights (mass M) can be screwed on the bar at equal distances R from the axis of the pulley. In each trial, the distance R is increased.

1. If we were to do an experiment with a bar that uniformly lost mass through the course of a single trial, how would the angular acceleration and the moment of inertia of the system change?
2. If were were to repeat the experiment with a bar that lost mass from the ends through the course of a single trial of the experiment, how would the angular acceleration and the moment of inertia of the system change?
3. If were were to repeat the experiment with a pulley that's radius decreased during the course of a trial, how would the angular acceleration and the moment of inertia of the system change?

2. Relevant equations
angular acceleration = angular momentum/moment of inertia
moment of inertia = mr^2

3. The attempt at a solution
1. The angular acceleration would increase because the moment of the inertia decreases as the mass of the bar decreases.
2. I'm not sure...
3. The angular acceleration would increase because the moment of inertia decreases since the radius of the pulley decreases.

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