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Kinetic Energy loss in a completely inelastic collision

  1. Feb 26, 2012 #1
    1. The problem statement, all variables and given/known data

    A particle of mass m[itex]_{1}[/itex] and speed v[itex]_{1}[/itex] collides with a second particle of mass m[itex]_{2}[/itex] at rest. If the collision is perfectly inelastic what fraction of the kinetic energy is lost in the collision? Comment on your answer for the casses that m1 is much much smaller than m2 and vice versa.

    2. Relevant equations

    KE = [itex]\frac{1}{2}[/itex]mv[itex]^{2}[/itex]

    3. The attempt at a solution

    m[itex]_{1}[/itex]v[itex]^{2}_{1}[/itex] = (m[itex]_{1}[/itex]+m[itex]_{2}[/itex])v[itex]^{2}_{f}[/itex]

    if this is right... not really sure how to show as fraction of lost kinetic energy :/
  2. jcsd
  3. Feb 26, 2012 #2


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    Staff: Mentor

    Keep in mind that momentum is ALWAYS conserved. So you should be able to find an expression for Vf in terms of the masses and V1. Then you'll be able to directly compare the initial and final kinetic energies.
  4. Feb 26, 2012 #3
    Thank you :) i think i got it
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