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Homework Help: Elastic collision in two dimensions

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

    On a frictionless surface, a 0.35 kg puck moves horizontally to the right (at an angle of 0°) and a speed of 2.3 m/s. It collides with a 0.23 kg puck that is stationary. After the collision, the puck that was initially moving has a speed of 2.0 m/s and is moving at an angle of −32°. What is the velocity of the other puck after the collision?

    2. Relevant equations
    Momentum before= momentum after
    kinetic energy before= kinetic energy after
    AB=AB cos (x)

    3. The attempt at a solution

    From Momentum before= momentum after, I got
    M1=first mass
    Vi1=initial velocity of the first mass
    Vf1=final velocity of the first mass...and I think you get the rest

    From the kinetic energy before= kinetic energy after, i got

    Now i'm kinda lost on what to do...some advice?
    Last edited: Dec 3, 2007
  2. jcsd
  3. Dec 3, 2007 #2
    ok so you have one puck moving straight to the right initially. this has a certain momentum. this certain momentum is equal to the momentum of both of the pucks after the collision (which you already stated)

    initial momentum = .35 x 2.3 = .805 to the right (0 degrees)

    if you know that one will move at -32 degrees with a velocity of 2 so determine its momentum. all you have to do now is find the other momentum vector that, when added to this one, will equal .805 at 0 degrees.
    Last edited: Dec 3, 2007
  4. Dec 3, 2007 #3
    i got it, thanks
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