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Homework Help: Perfectly elastic collision

  1. Dec 2, 2008 #1
    1. The problem statement, all variables and given/known data
    In an isolated system, cart1 (with mass = 1 kg and vi1 = 2) has a perfectly elastic collision with cart2 (with mass = 2 kg and vi2 = 0). Find the velocity of cart1 and the velocity of cart2 after the collision.

    2. Relevant equations
    1/2m1vi12 + 1/2m2vi22 = 1/2m1v1f2 + 1/2m2v2f2

    m1vi1 + m2v2i = m1v1f + m2v2f

    3. The attempt at a solution

    I plugged in all of the numbers.

    For momentum I got
    2= V1f + 2 V2f

    For kinetic energy I got
    4 = V1f2 + 2V2f2

    Next I solved for V1f and plugged it into the equation.

    I just need some confirmation that my answer is right.

    It doesn't seem correct.

    I got:
    V2f = 2
    V1f = -2
  2. jcsd
  3. Dec 2, 2008 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    You could check your answers yourself. Do they satisfy both the kinetic energy and momentum equations?
  4. Dec 2, 2008 #3
    No, they don't. You're right that was an easy way to check myself.
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