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Homework Help: Conservation of angular momentum on low-friction bearings

  1. Mar 5, 2008 #1
    1. The problem statement, all variables and given/known data

    Two disks are mounted on low-friction bearings on the same axle and can be brought together so that they couple and rotate as one unit. a) The first disk, with rotational inertia 3.3 kg m^2 about its central axis, is set spinning at 450 rev/min. The second disk, with rotational inertia 6.6 kg m^2 about its central axis, is set spinning at 900 rev/min in the same direction as the first. They then couple together. What is their angular speed after coupling?



    2. Relevant equations

    L = L'
    L = Iw



    3. The attempt at a solution

    Can I get some hints on how to find the final rotational inertia? I'm sure it's something simple; I've just sort of been struggling with this chapter. I can't seem to visulize angular momentum at all.
     
  2. jcsd
  3. Mar 5, 2008 #2

    Doc Al

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    Staff: Mentor

    The rotational inertia of the coupled disks is just the sum of the individual rotational inertias of each disk.
     
  4. Mar 5, 2008 #3
    Then what is the initial rotational inertia?
     
  5. Mar 5, 2008 #4

    Doc Al

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    Staff: Mentor

    The rotational inertia of each disk is given.

    Hint: The total angular momentum is the sum of the angular momenta of each disk. (I suspect that's the question you meant to ask.)
     
  6. Mar 6, 2008 #5
    Oh I see. I feel dumb, now.
     
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