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Homework Help: Conservation of momentum

  1. Nov 23, 2008 #1
    1. The problem statement, all variables and given/known data
    Two hockey puck of equal mass undergo a collision on a hockey rink. One puck is initiall at rest while the other is moving with a speed of 5.4m/s. After the collision, the velocities of the pucks make angles of 33 and 46 (degrees) relative to the initial velocity of the moving puck. Determine the speed of each puck after the collision.

    2. Relevant equations

    3. The attempt at a solution

    We have tried several failed approaches. The correct answer is 3m/s and 4m/s. What is confusing us is that the momentum should be conserved. So the sum of the two final momentums should be that of the initial momentum. Thanks in advance,
  2. jcsd
  3. Nov 23, 2008 #2
    Bump. Can anyone explain this? My friend and I have a test tommorow and we still don't see how this is possible. Thanks.
  4. Nov 23, 2008 #3


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    It is conserved. momentum is a vector quantity. The initial momentum is to the right. The final momentum, the vector sum of the 2 pucks after the collison, must be equal to and in the same direction as the initial momentum.
  5. Nov 23, 2008 #4
    Ahhh I see. So What I've done is drawn the two vectors as two sides in a triangle, with the third side being the initial momentum vector. Then I solved with sin law. Thanks for the post!
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