# Rolling without slipping

1. Sep 5, 2010

### raisatantuico

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

a solid metal ball of mass M and radius R is rolling without slipping down and incline. A static friction force of magnitude f is acting on the ball. What is the magnitude of the torque due to static friction?
a.) zero b.) rfcos theta c.) rfsin theta d.)Rf e. MRF

2. Relevant equations

ki+ui=kf=uf (conservation of energy)

3. The attempt at a solution
since the ball is rolling without slipping, why is there friction involved? do we just simply ignore friction, so the answer will just be the definition of torque: rfsin theta ?

2. Sep 5, 2010

### Staff: Mentor

Without friction, the ball would slide not roll.
No, you cannot ignore friction. (And how is that answer ignoring friction anyway? It includes f!)

3. Sep 5, 2010

### raisatantuico

f in the equation is force. torque= radius x force sin theta. net torque is also equal to angular acceleration x moment of inertia

where does friction come in this defintion of torque?

4. Sep 5, 2010

### Staff: Mentor

Here 'f' is the friction force. (What direction does friction act? What angle does it make with the radius?)