# Rotational motion problems involving radians

1. May 5, 2013

### lorkp

1. The problem statement, all variables and given/known data
The professor gives us an exam preview where he hints at the types of problems via the picture. Attached is the preview. I have a question about pictures 1 and 2. It's probably a problem that involves rotational and translational energy, conservation of energy. If it's rolling without slipping, it would mean a torque problem. What's throwing me off, however, is that he shows that there's a 90 degree angle. But I don't have a concrete reason for why it's applicable. It could do with radians traveled and so it could be a work problem because work = torque * delta theta. However the friction force that provides the torque would be changing because the normal force would be changing, correct? I'm not sure how to account for that.

Any other ideas for a rotational problem that would involve radians?

Thank you

2. Relevant equations

3. The attempt at a solution

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2. May 5, 2013

### tiny-tim

welcome to pf!

hi lorkp! welcome to pf!
he's simply telling you that the initial angle is 45° (or 135°)

anwyay, since it looks as if the ball is going to be gently nudged into the arc, it looks to me like an shm question