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Help with rotational dynamics

  1. Jan 30, 2012 #1
    1. The problem statement, all variables and given/known data

    Translation: Determinate, for the system of Fig. 10-39 the angular velocity of the disk and the linear velocity of m and m'. Calculate the tension in each string. Suposse that m = 600 g, m' = 500 g, M = 800 g, R = 8 cm and r = 6 cm.

    2. Relevant equations

    3. The attempt at a solution
    The problem is I don't know to get the moment of inertia because I have the mass of one disk only.
  2. jcsd
  3. Jan 30, 2012 #2


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    Gold Member

    I agree, it looks like you were not given enough information.

    One could assume that M was for both discs, but you would still need to know the thicknesses of the two discs which you could estimate if you had to.

    Bad problem.
  4. Jan 31, 2012 #3


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    Homework Helper

    Solve the problem assuming that M is the mass of the whole pulley that consist of two disk-form parts of the same thickness, made of the same material. Usually the problem writers think in 2D where thickness does not exist.:wink:

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