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Homework Help: New Angular Velocity

  1. Oct 23, 2008 #1
    The mass of a star is 1.1e31 kg and its angular velocity is 1.40×10-7 rad/s. Find its new angular velocity if the diameter suddenly shrinks to 0.17 times its present size. Assume a uniform mass distribution before and after. [Icm for a solid sphere of uniform density is 2/5 mr^2].

    i have to use I1w1=I2w2

    it is (2/5)mr^2w1=(2/5)mr^2w2 and find out my w2

    but i have all the data unless the r.

    what i should put in r?...
  2. jcsd
  3. Oct 23, 2008 #2


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    Don't put anything in for r. Leave it 'r'. If the initial radius is r then the final radius is 0.17*r. The r itself will cancel. If they don't give you a value for a number, it's a pretty sure bet that you don't even need to know it since it will cancel out from both sides of the equation.
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