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Help! elastic collistion, cons of momentum problem!

  1. Dec 18, 2012 #1
    Block 1 moves with speed of 10m/s to right. It hits block 2 which has twice the mass of block 1 and speed of 5m/s to right. compute the magnitude and direction of block 1 for a perfectly elastic collision.


    u1 = 10m/s
    u2 = 5m/s

    m1v1 + m2v2 = m1u1 + m2u2 ---->
    v1 + 2v2 = u1 + 2u2
    ............= 10 + 2(5) = 20

    (1) v1 + 2v2 = 20

    why did u2 and v2 get multiplied by two and why did the m cross out?
  2. jcsd
  3. Dec 19, 2012 #2


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    Are you saying you've just copied these steps from somewhere else and don't know the logic behind them? If those steps were your own work, surely you know why you made them.
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