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Homework Help: Elastic Collision Problem - pretty sure my answer isn't right.

  1. Oct 30, 2012 #1
    1. The problem statement, all variables and given/known data
    Walt and Wolfie collide in bumper cars of mass 50 kg each. Walt has a mass of 78 kg, and Wolfie has a mass of 61 kg. Walt strikes Wolfie from the rear at V = 3.7 m/s. If the collision is elastic, Wolfie is initially at rest, and Walt's final speed is 0.2655 m/s in the same direction, what is Wolfie's speed after the collision?

    2. Relevant equations
    m1*(u1^2)/2 = m1*(v1^2)/2 + m2*(v2^2)/2

    3. The attempt at a solution
    78*(3.7^2)/2 = 78*(0.2655^2)/2 + 61*(x^2)/2
    and I get 4.17 m/s, but that doesn't seem right to me.
    Can anyone shed some light on this for me?
  2. jcsd
  3. Oct 30, 2012 #2
    Why doesn't 4.17 m/s sound reasonable to you?
  4. Oct 30, 2012 #3
    Then Wolfie's speed after the collision is higher than the velocity that Walt hit Wolfie with initially, which doesn't seem right.
  5. Oct 30, 2012 #4


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    What happened to the mass of the bumper cars themselves?
  6. Oct 30, 2012 #5
    Along SteamKing's lines, remember that the bumper cars are part of the kinetic energies we're talking about. With that said, Wolfie is less massive that Walt, so might it be conceivable that he's going faster than Walt was? We're talking about energy conservation, not velocity conservation.
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