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Angular momentum

  1. Jun 26, 2011 #1
    Hi to all,

    the question is:


    the two sticks clash and stick one to the other, the plane is smooth friction.
    the momentum of one stick (in it's own center of mass is 0.5*L^2*m).

    the length of the sticks is L and the mass is m, the vertical's stick speed is v.

    I have to find the angular speed (w- omega) that both sticks will rotate in, I have manged to do this with the angular momentum preservation law, and I would like to know how to this with energy preservation law.

    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Jun 26, 2011 #2
    ok... my bad!!
    the energy is not the same before and after the clash- it is not an elastic clash
  4. Jun 26, 2011 #3


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    welcome to pf!

    hi vlio20! welcome to pf! :smile:
    you can't :redface:, it isn't! :biggrin:

    (mechanical) energy is never conserved unless the question says so

    in this case, it obviously isn't conserved, because the two bodies stick together, so it's a perfectly https://www.physicsforums.com/library.php?do=view_item&itemid=38"

    https://www.physicsforums.com/library.php?do=view_item&itemid=53" and energy are enough to solve a problem … any extra equation (like a geometrical constraint) means that something has to go, and that's always the energy equation :wink:
    Last edited by a moderator: Apr 26, 2017
  5. Jun 26, 2011 #4


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    Last edited by a moderator: Apr 26, 2017
  6. Jun 26, 2011 #5


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    oops! :biggrin:
  7. Jun 26, 2011 #6
    yes I have understand my mistake after I posted it.
    the collision is a plastic and not elastic

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