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Homework Help: Elastic Collision - two carts

  1. Dec 1, 2011 #1
    1. The problem statement, all variables and given/known data
    Two carts equipped with spring bumpers on an air track have an elastic collision. The 253-g cart has an initial velocity of 1.80 m/s [N]. The 232-g cart is initially stationary. What is the velocity of each cart after the collision?

    2. Relevant equations
    I know because cart 2 is initially stationary:
    m1v1 = m1v1' + m2v2'
    and 1/2m1v1^2 = 1/2 m1v1'^2 + 1/2m2v2'^2

    3. The attempt at a solution
    I've been trying to solve this by rearranging the equations and subbing them in to each other, but I keep ending up with really complicated equations that I can't seem to solve. Is there a simpler way to look at a problem like this? I'm fine with most collisions that aren't elastic, but the ones that are I can't do. Thanks.
  2. jcsd
  3. Dec 1, 2011 #2
    With regards to the spring bumpers, was there any given information in the problem about the spring constants?
  4. Dec 1, 2011 #3
    Nothing. I posted the question verbatim, and there was no diagram either.
  5. Dec 1, 2011 #4


    User Avatar

    Staff: Mentor

    The squares of the velocities in the KE formula can definitely complicate things algebraically. Another relationship that you can use in place of it (and is derivable from the conservation of momentum and KE) is that the relative velocities of the two objects after collision is equal to the negative of the relative velocities before the collision. Using variables, suppose that the initial velocities of the objects are v1 and v2, and the final velocities are u1 and u2. Then

    (u2 - u1) = -(v2 - v1)

    That should make your life *much* easier!
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