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Homework Help: Three Disks Coupled by Two Belts

  1. Mar 25, 2014 #1
    1. The problem statement, all variables and given/known data
    The figure below shows three rotating, uniform disks that are coupled by belts. One belt runs around the rims of disks A and C. Another belt runs around a central hub on disk A and the rim of disk B. The belts move smoothly without slippage on the rims and hub. Disk A has radius R; its hub has radius 0.6000R; disk B has radius 0.2000R; and disk C has radius 1.500R. Disks B and C have the same density (mass per unit volume) and thickness. What is the ratio of the magnitude of the angular momentum of disk C to that of disk B?
    Image: http://www.webassign.net/hrw/W0249-N.jpg

    2. Relevant equations
    L=mvr=Iw (w is angular speed)

    3. The attempt at a solution
    Honestly I have no clue how to even start this...
    I think that the density will somehow give me mass to plug into equation for I, which can then be plugged into L. But I don't know how to get w or v and without those I don't know how to get L.
  2. jcsd
  3. Mar 25, 2014 #2
    Could the w's for each disk all be directly proportional to one another?

    I think you are right about the density.
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