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Homework Help: Ball rolling down an incline

  1. Oct 17, 2009 #1
    1. The problem statement, all variables and given/known data

    A ball of mass 2.80 kg and radius 0.153 m is released from rest on a plane inclined at an angle θ = 41.0° with respect to the horizontal. How fast is the ball moving (in m/s) after it has rolled a distance d=1.60 m? Assume that the ball rolls without slipping, and that its moment of inertia about its center of mass is 1.80E-2 kg·m2.

    2. Relevant equations

    I = Icm + M(d^2)......parallel-axis theorem

    wf ^2 = wi^2 + 2a(thetaF - thetaI).....constant angular acceleration

    theta = S/r


    3. The attempt at a solution

    I think I need to use the parallel-axis theorem to solve for one step in the problem, so.....

    I = 0.0180 + 2.8(1.6^2) = 7.186 kg * m^2

    Next I found how many "radians" the ball travels in 1.6 m...

    C = 2"pi"r = 2"pi" * .153m = .936 m (circumference of ball)

    1rad = .936 m

    1.6m * (1rad/.936m) = 1.7 radians

    I am not even sure how to solve this problem....I did the above equations so I could see if I was going on the right track by a process of elimination...usually I dont worry about the actual numbers untill the end of the problem...i.e. if I just use the units in the equations and my "answer" is in the correct units it usually means I am on the correct path....Please help me solve this problem...
  2. jcsd
  3. Oct 17, 2009 #2


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    Homework Helper

    Apply the conservation of energy.
    The potential energy = Translational kinetic energy + rotational kinetic energy.
    Angle is given, displacement along the inclined plane is given. From that find height through which the ball rolls.
  4. Oct 19, 2009 #3

    mg(d*sin(theta)= .5m *v^2 + .5I(v/r)^2
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