# Torque and frictional force

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1. Mar 1, 2015

### Joe Armas

1. The problem statement, all variables and given/known data
In the picture

2. Relevant equations
Torque = I * Alpha
Alpha = a / r
Fnet = m*a

3. The attempt at a solution
I provided my work in the pictures. I figured out that the frictional force in system B is greater than in system A. I am not sure how to compare this with the frictional force from system C. I figured out the sum if the frictional forces of A and B are equal to mg sin theta, but don't know how the two compare.

2. Mar 1, 2015

### TSny

Answers to (a) and (b) look good to me. According to (b), objects B and C have the same net force. Look at your free body diagrams for objects B and C. If you add the forces in the diagram for B do you get the same net force as the diagram for C?

What should be the direction of the friction force on C to make it rotate in the right direction for rolling down the plane?

3. Mar 1, 2015

### Joe Armas

So Friction force on C is pointing up the ramp and its magnitude is equal to friction force on B? The frictional force on C is kinetic not static correct?

4. Mar 1, 2015

### TSny

Yes, that's the only way Fnet,B can equal Fnet,C.

To answer this, remember that the statement of the problem says that C rolls without slipping.