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Homework Help: Sphere rolling down a ramp

  1. Nov 15, 2011 #1
    1. The problem statement, all variables and given/known data

    A hollow sphereical shell rolls without slipping down a 38 degree slope, mass 2kg, find the acceleration the friction force and the minimum coefficent of friction needed to prevent slipping

    2. Relevant equations

    mgh, E=1/2mv^2=1/2Iw^2

    3. The attempt at a solution

    i dont really know where to start, i know moment of inertia will affect how fast this will accelerate due to gravity but im not given it so i dont know to solve it, hints would be great please!
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Nov 16, 2011 #2


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    the gravity provides the ball with a torque which is mg*cos(38)
    when the friction is big enough to cancel out the turning effect caused by the torque
  4. Nov 16, 2011 #3
    How can this be a torque when the units are wrong?
  5. Nov 16, 2011 #4
    Time for some hints. First of all write an equation energy of the object when it has moved an arbitrary distance (D) along the slope.

    Next, determine the torque that causes the ball to rotate.

    Think about whether acceleration will be a constant. Based on your decision, more equations of motion might come to mind.
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