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Spring Loaded Collision, help

  1. Jun 13, 2010 #1
    Spring Loaded Collision, help!!

    [PLAIN]https://wug-s.physics.uiuc.edu/cgi/courses/shell/common/showme.pl?cc/DuPage/phys2111/summer/homework/Ch-09-10/IE_spring_loaded_collision/springloadedcollision.gif [Broken]

    1. The problem statement, all variables and given/known data
    A cart with mass m1 = 3.2 kg and initial velocity of v1,i = 2.1 m/s collides with another cart of mass M2 = 4.3 kg which is initially at rest in the lab frame. The collision is completely elastic, and the wheels on the carts can be treated as massless and frictionless. What is the velocity of m1 after the collision in a coordinate system where the center of mass of the two carts is not moving (the "center of mass frame") ?

    2. Relevant equations

    p = mv
    m1v1 = m2v2

    3. The attempt at a solution

    i used m1 = 3.2
    m2 = 3.2+4.3
    v1 = 2.1
    v2 = v

    so i had, (3.2)(2.1) = (3.2+4.3)v
    when i solved for v i got 0.896, but this isnt right, so i dont know what its asking for.
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Jun 13, 2010 #2
    Re: Spring Loaded Collision, help!!

    i guess what i need to know is how to find the velocity of the center of mass
  4. Jun 13, 2010 #3
    Re: Spring Loaded Collision, help!!

    nevermind, i solved it.

    velocity of center of mass was the value i got before (0.896). to solve for the final velocity of m1, i had to do vi - vcm (2.1 - 0.896).

    Thanks anyway!
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