# Conservation and angular velocity

## Homework Statement

I need help with this question: http://img804.imageshack.us/img804/2278/unledsbg.jpg [Broken]

For a, I got omega = 18.63 rad/s by using methods of conservation of energy. Can someone tell me if I did this right? If not, please help me out! To be honest, I thought I had to use conservation of momentum for this since it involves a collision, but its equations dont involve angular velocity.

## Homework Equations

Conservation of energy/momentum

## The Attempt at a Solution

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Doc Al
Mentor
Energy is not conserved. But angular momentum is.

So does that mean I find v by means of conservation of momentum, and then use omega = v / r to find the answer? The reason I'm confused is because at the note at the bottom of the question, it says treat the door as a rod rotating about its end, which is a hint to use Inertia = (1/3)ML^2. Conservation of energy, not momentum, has inertia in its equation.

Doc Al
Mentor
Conservation of energy, not momentum, has inertia in its equation.
Conservation of angular momentum will involve the moment of inertia.