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Rolling without slipping help

  1. Nov 28, 2006 #1
    I can't figure out this problem. Pretty much totally lost. It has a hollow, spherical shell with a mass of 2kg, rolls without slipping down an incline of 38 degree's. It wants me to find the acceleration, the friction force, ane the minimum coeffcient of friction needed to prevent slipping.

    The examples in my book and the equations all seem to have the Radius in them, and my problem doesn't give a radius. The equation that is has is Vcm=Rw.
    So i'm not sure what to do when I don't have the radius and only the mass.
    Since is says it is a hollow sphere, am I supposed to do something with the motion of inertia ? With K=1/2Mv^2+1/2Iw^2 ?

    And then I don't know how I'm supposed to find the frictional force and the coeffcient of friction. g(sinθ-μcosθ)=a ?
  2. jcsd
  3. Nov 28, 2006 #2


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    Staff: Mentor

    It helps if you use the homework posting template that is provided. Please use it next time.

    Yes, you need to use the moment of intertia. The friction force supplies the rotational energy for the cylinder. The cylinder will acquire both translational and rotational energy, as the equation you've written indicates.
  4. Nov 28, 2006 #3


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    Science Advisor
    Homework Helper

    Just assume the radius is R to get started. You are right, the linear and rotation velocities are linked by V(center of mass) = R.omega.

    R will appear in other places as well (e.g. the moment of inertia). With luck, all the R's will cancel out in the end.
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