Rolling with no slipping problem

[Ianray]

This is my first time posting here, and I was hoping someone can help me with a problem on my homework.

A solid ball is released from rest and slides down a hillside that slopes downward at 65degrees from the horizontal. a) What minimum value must the coefficient of static friction between the hill and ball surfaces have for no slipping to occur? b) Would the coefficient of friction calculated in (a) be sufficient to prevent a hollow ball (such as a soccer ball) from slipping? Justify your answer. in part (a), why did we use the coefficient of static friction and not the coefficient of kinetic friction?

This problem just makes absolutely no sense to me, I can do every other one on the homework but I have no idea how to even start this. Also I don't understand what the difference between slipping and no-slipping is? Thanks.

 

[Doc Al]

Slipping means that the surfaces slide against each other--think of a tire leaving a tread mark. No slipping means it rolls but doesn't slide. What's the condition for rolling without slipping?

Hint: First solve for the friction force needed.

Use Newton's 2nd law and the condition for rolling without slipping.

 

[Ianray]

OK, thanks a lot, I finally got the right answer, it certainly helped once I knew aR = a when there's no slipping. You're an awesome person for taking the time to help all of us.