Elastic Cart Collision of a stationary and a moving cart

  1. I'm having some trouble with some homework and I'm hoping someone can help me.

    PROBLEM:
    #6. Cart1, with mass m, is initially at rest and is struck by cart2,
    which has a mass of 336 kg and initial speed of 1.81 m/s. The collision
    is elastic and after the collision cart2 continues to move in its
    original direction at 0.807 m/s. Find m, the mass of cart1.
    #7.Find the speed of cart1 after the collision.

    ATTEMPT AT SOLUTION:

    I have calculated that

    m1v1+m2v2=m1v1'+m2v2'
    m1(0)+336kg(1.81m/s)=m1v1'+336kg(0.807m/s)
    m1v1'=336kg(1.81-0.807)
    m1v1'=337 kg*m/s

    I'm stuck here. I tried calculating the amount of energy the second
    cart should have

    1/2m2(v2-v2')^2=
    0.5(336)(1.81-0.807)^2=169J

    and then that

    169J=0.5m1(v1)^2 so that

    m1=169*2/v1^2

    and subbing that into

    m1v1'=337 kg*m/s

    (169*2/v1'^2)*v1'=337 kg*m/s

    338/v1'=337

    thus v1' =338/337

    This however does not answer #7 and when working backwards to find the
    mass it also provides the wrong answer.

    Thank you for any assistance you can provide.

    Sincerely,

    Potato21


    EDIT: Oops, dumb mistake, I got it!
     
    Last edited: Jan 16, 2011
  2. jcsd
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