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Homework Help: Momentum elastic colliion in 2D

  1. Nov 17, 2011 #1
    1. The problem statement, all variables and given/known data
    A hockey player of mass 8.0x10 kg was skating at a velocity of 7.5 m/s [E] when he accidentally hit a linesman who was just standing on the ice. The mass of the linesma is 9.0x10 kg and his velocity after the collision was 3.0 m/s [N30°E].
    a) find the velocity of the hockey player after the collision
    b) find the kinetic energy lost during the collision

    2. Relevant equations

    0.5mv2 = v

    3. The attempt at a solution

    since momentum is conserved: (horizontal E (+) direction)
    mAvA + mBvB= mBvB' + mAvA'
    80kg(7.5m/s) + 0kgm/s = 90cos 30° + 80vAcosθ
    600-90cos30°= 80vAcosθ
    (600-90cos30°)/80 = vAcosθ
    6.5 m/s = vAcosθ

    I'm not really sure about what to do next, do i just continue with finding the vAsinθ for the same direction and then do the same things for the vertical direction? Are there any other solid steps that i need to know in order to solve a 2D momentum question?
  2. jcsd
  3. Nov 18, 2011 #2
    What you have done is correct for the momentum in the E direction.
    You now need to do a similar thing for the momentum in the N direction for the linesman and the equivalent momentum in the S direction for the player.
    This will involve the Sine30 and the Sine∅
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