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Homework Help: Another Torque Question

  1. Jul 9, 2007 #1
    1. The problem statement, all variables and given/known data

    Consider a circular wheel with a mass m, and a radius R. The moment of inertia about the center of the wheel is I = kmR^2, where k is a constant in the range between 0.5<k<1.0. A rope wraps around the wheel. A weight of mass 2m is attached to the end of this rope. At some moment, the weight is falling with a speed v. The total kinetic energy K of the system at this moment is given by what mathematical equation?

    2. Relevant equations

    K = 1/2 mv^2

    3. The attempt at a solution

    I know that the mass of the wheel will have to be considered to find the final kinetic energy...can someone please give me a hint what to do next?
  2. jcsd
  3. Jul 9, 2007 #2


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    Use [tex] E_{k(rotational)} = \frac{1}{2} I \omega^2 [/tex], then add the translational kinetic energy term to it. This would give the total kinetic energy. Energy terms in classsical mechanics are hardly ever multiplied or divided, so what's left to do is add or take away. In this case, since it's a total one wants, one adds.
    Last edited: Jul 10, 2007
  4. Jul 10, 2007 #3
    thank you so much!
  5. Jul 10, 2007 #4
    V=rw. Net T=T(rotational) + T(translational)
  6. Jul 10, 2007 #5
    How about this?? It's the second part to the question....

    Assume that k=1/2

    QUESTION....If this system is released from rest, find the speed, v, at the moment when the weight has descended a vertical distance h. Any help would be nice.

  7. Jul 11, 2007 #6


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    Homework Helper

    obviously your relevant equations 2 are incomplete, otherwise you would have your answer... what other relevant equations are there?
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