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Elastic Collision

  1. May 5, 2009 #1
    1. The problem statement, all variables and given/known data
    The problem is in the picture(attached)

    2. Relevant equations
    I know we have to use
    m1v1 + m2v2 = m1v1' + m2v2'
    (1/2)m1v1^2 + (1/2)m2v2^2 = (1/2)m1v1'^2 + (1/2)m2v2'^2

    3. The attempt at a solution
    All I know is that it needs to be split up into components.
    Please help me out.

    Attached Files:

    • ps.jpg
      File size:
      35.1 KB
  2. jcsd
  3. May 6, 2009 #2


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    Homework Helper

    Welcome to PF!

    Welcome to PF! :smile:

    (please type the question in future … it's much easier to read than having to look at a picture in a separate window)

    (and try using the X2 and X2 tags just above the Reply box :wink:)

    Yes, the first equation is a vector equations, and needs to be split up into two scalar equations.

    (You could choose West and North for the component directions, for example.)

    So … show us what you get. :smile:
  4. May 6, 2009 #3
    Health Warning::smile:

    This problem can get very messy unless you translate it into
    the reference frame in which the c of m is stationary.

  5. May 6, 2009 #4


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    No, you should be able to do it in the reference frame given.
  6. May 6, 2009 #5
    Thanks guys, and yes I will try this question out. I got some help today from a friend, he said that there was no need for NS/EW components. He told me to make a triangle. So therefore the resulting velocity after the collision of the 2amu mass would be v1'cos10.

    2(2km/s) + 1(0m/s) = 2(v1'cos10) + v2'
    4 - 2v1'cos10 = v2' (this will be equation one)

    We know kinetic energy is conserved:
    2(2km/s)2 + 1(0m/s)2 = 2(v1'cos10)2 + v2'2
    8 - 2(v1'cos10)2 = v2'2 (our second equation)

    Then sub in equations into each other for v2'.
    I have to go for now but I will get back to you guys soon on the problem. Please keep in mind that im only in grade 12:confused:. Thanks again.
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