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Homework Help: Quick Momentum Question

  1. Jun 16, 2010 #1
    1. The problem statement, all variables and given/known data

    I'm given the masses of two objects, m1 and m2. The kinetic energy K is equal in both objects. It wants to know which object has the greater magnitude of momentum.

    2. Relevant equations

    K = 1/2mv^2 (Kinetic Energy)
    p = mv (Momentum)
    K = p^2/2m (K in terms of p)

    3. The attempt at a solution

    Now, I know that I have two variables to solve for before I can answer the question. I need to find v1 and v2. Finding one of those in terms of the other is easy, but that only leaves me with one equation and two variables. I can't for the life of me remember what relationship I can use to give me a second equation and my book isn't much help at all.
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Jun 16, 2010 #2
    Why don't you just equate the two

    [tex]K_1 = K_2[/tex]


    Since you know the masses you just solve for one and see which one is greater. If p1^2=2p2^2 then p1 is obviously greater. :) You could take the square root too if you really wanted to get the right scale factor between the momentums.
  4. Jun 17, 2010 #3
    Wow, do I feel stupid. You're right. I don't need an answer at all, just a ratio. I think I was blinded by a collision example done in class where the teacher did some sort of long problem where the solution wasn't immediately obvious. Thanks, Mindscrape.
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