# Homework Help: Rotational dynamics, semicircular arc

1. Jan 15, 2013

### Saitama

1. The problem statement, all variables and given/known data
(see attachment)

2. Relevant equations

3. The attempt at a solution
Do I need to take torque about C here?

Any help is appreciated, Thanks!

#### Attached Files:

• ###### semicircular arc.jpg
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2. Jan 15, 2013

### Simon Bridge

How else would you find the angular acceleration?

3. Jan 15, 2013

### Saitama

I asked this because I am sure this would involve integrals and before doing the maths, I want to be sure if I am heading in the right direction.

4. Jan 15, 2013

### Simon Bridge

If you can only think of one way to do a problem, it is worth a try: give it a go.
Everything involves an integral if you don't already know the result.

But it can help to have a think about the problem before starting:
* If $\beta=0$, what is the initial angular acceleration?
* How does the total mass vary with $\beta$?
* How does the location of the center of mass vary with $\beta$?

5. Jan 15, 2013

### Saitama

I have solved the problem, I had trouble because I misinterpreted the problem. It looked to me like a semicircular arc but it isn't. Thanks!

6. Jan 15, 2013

### haruspex

Yes, it's a poor drawing. The point where those angles meet doesn't look like it's supposed to be the centre of the arc.