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Homework Help: Elastic collision

  1. Sep 30, 2010 #1
    1. The problem statement, all variables and given/known data
    This is an exam prep question

    Particle A has mass 3m and velocity i + 2j, it collides with particle B mass m velocity -i + j. Collision is elastic. After collision Particle A is observed to be moving along the +ve y-axis. Find the final speeds of the two particles.(two possible cases)

    2. Relevant equations
    Being elastic the kinetic energy is the same before the collision and after.
    We are given the answers ([tex]3/2,\sqrt{41}/2[/tex] or [tex]2,\sqrt{5}[/tex].

    3. The attempt at a solution
    Could someone give me a little nudge in the right direction? I can't see where to begin, what is the state of B after the collision?

  2. jcsd
  3. Sep 30, 2010 #2


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    Homework Helper

    Right, so you can form the conservation of kinetic energy equation.

    You also need to use conservation of linear momentum. Momentum before = momentum after.

    Since you do not know the magnitudes of the final velocities, here is how I put them as

    vAj and vBi + βj
  4. Sep 30, 2010 #3
    Thanks for the reply.

    I got that far but can't see how to proceed.
  5. Sep 30, 2010 #4


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    Homework Helper

    As rock.freak suggested write up the equations for both the x and y components of the momentum.

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