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Homework Help: Alpha Particle Elastic Collisions

  1. Nov 1, 2012 #1
    1. The problem statement, all variables and given/known data

    A proton strikes a stationary alpha particle (4He nucleus) head-on. Assuming the collision is completely elastic, what fraction of the proton’s kinetic energy is transferred to the alpha particle?

    2. Relevant equations

    Pi = Pf
    Ki = Kf

    3. The attempt at a solution
    For Pi = Pf
    mv = m1v1 + 4m2v2
    cancel the m's out
    v = v1 + 4v2

    For Ki = Kf
    1/2mv^2 = 1/2m1v1^2 + 1/2(4)m2v2^2
    Cancel out the 1/2 and the m's

    v^2 = v1^2 + 2v2^2

    Now I'm lost.. can't substitute it into the equation, I feel like I got nowhere.

    Help please.
  2. jcsd
  3. Nov 2, 2012 #2


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    Homework Helper

    The second equation is not correct. It should be v^2 = v1^2 + 4v2^2
    You can substitute v1=v-4v2 into it.

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