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Homework Help: Angular momentum problem

  1. May 3, 2007 #1
    1. The problem statement, all variables and given/known data

    Two masses M each are connected by a rigid rod of negligible mass having length a.The CM of the system is stationary in a gravity free space and the system rotates about the CM. with angular velocity w.One of the rotating masses strikes a third stationary ball of mass M which sticks to it.What is the angular momentum of the three mass system before and after collision?

    2. Relevant equations

    3. The attempt at a solution

    For the collision conservation of linear momentum will be applicable.
    Mv=2Mv' or,v'=v/2=wa/4. From this w' can be calculated.

    Prior collision,L=Iw where I is the MI of the two mass system.

    After collision, L'=I'w'

    Please check if I am correct.
  2. jcsd
  3. May 3, 2007 #2


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    Homework Helper

    the system will rotate about new center of mass. Check for the position of new center of mass!!
  4. May 3, 2007 #3
    So,we are to be careful to calculate I for the second time.
    Second time, CM will be a/3 rd distance away from the mass 2M.Accordingly,I will change.

    But angular velocity would be same as w'.Right?
  5. May 3, 2007 #4
    There will be no linear momentum...
    angular momentum will be conserved...
    CM will change the position...
    And if one wants to find w',one has to find I' carefully.
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