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Homework Help: Conservation of Angular Momentum of Star

  1. Nov 4, 2008 #1
    1. The problem statement, all variables and given/known data
    The mass of a star is 1.51·1031 kg and its angular velocity is 1.50E-7 rad/s. Find its new angular velocity if the diameter suddenly shrinks to 0.49 times its present size. Assume a uniform mass distribution before and after. Icm for a solid sphere of uniform density is 2/5 mr2

    2. Relevant equations



    3. The attempt at a solution

    L(int) = [(2/5)M*R^2]*(wint)
    L(final) = [(2/5)M*(0.49)*R^2]*(wfinal)

    And I got stuck there. I dont know how to find the radius and I think thats holding me back.
  2. jcsd
  3. Nov 4, 2008 #2


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    Homework Helper

    Note that it will cancel out when you set them equal since you've expressed the final radius in terms of the initial radius.

    Be careful with the 0.49, it should be squared as well.
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