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Homework Help: Rolling without slipping

  1. Sep 5, 2010 #1
    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. jcsd
  3. Sep 5, 2010 #2

    Doc Al

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    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!)
     
  4. Sep 5, 2010 #3
    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?
     
  5. Sep 5, 2010 #4

    Doc Al

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    Staff: Mentor

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