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Homework Help: Energy Rotational Motion

  1. Nov 14, 2006 #1
    "Consider the bicycle wheel is not turning initially. A block of mass m is attached (with a massless string) to a wheel. The block is allowed to fall a distance of h. Assume that the wheel has a moment of inertia I about its rotation axis.

    Find the angular speed of the wheel after the block has fallen a distance of h in terms of m,g,h, r(of the wheel) and I"

    This is what I did:

    U + K + W(other) = U + K
    mgh + 0 + 0 = 0 + 1/2mv^2 + 1/2 I*omega^2

    omega = Sqrt[(2mgh - mv^2)/I]

    This is wrong... what am I doing wrong? I know I can use omega = v^2/r, but not sure where that would go...
  2. jcsd
  3. Nov 14, 2006 #2


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    Science Advisor
    Homework Helper

    ω = v^2/r is not correct, but it is sort of close. When you get it right, you can replace either v or ω using the correct relationship. Since you want to solve for ω, replace the v and solve away.
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