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Homework Help: Find Angular Momentum

  1. Jul 13, 2009 #1
    1. The problem statement, all variables and given/known data
    A small puck of mass 36 g and radius
    25 cm slides along an air table with a speed
    of 1.9 m/s. It makes a glazing collision with a
    larger puck of radius 59 cm and mass 85 g (ini-
    tially at rest) such that their rims just touch.
    The pucks stick together and spin around af-
    ter the collision.
    Note: The pucks are disks which have a
    moments of inertia equal to 1/2mR^2.
    What is the angular momentum of the sys-
    tem relative to the center-of-mass after the
    collision? Answer in units of kgm2/s.

    2. Relevant equations

    3. The attempt at a solution
    To be honest I have no idea. I tried several obviously ill-fated attempts. I have found the center of mass, and I know that it has to do with crossing the initial linear momentum with the new radius... I think...

    Any help would be greatly appreciated.
  2. jcsd
  3. Jul 14, 2009 #2


    User Avatar
    Science Advisor
    Homework Helper

    Welcome to PF!

    Hi shangri-la89! Welcome to PF! :smile:

    (have an alpha: α and an omega: ω and try using the X2 tag just above the Reply box :wink:)

    (oh, and it's a grazing collision … a glazing collision is when you walk into a glass door! :biggrin:)

    What is the angular momentum of the system before the collision?
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