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Homework Help: Need clarification: conservation of kinetic energy (elastic collision)

  1. Jul 23, 2008 #1
    if a block in motion hits one at rest, Ek1i = Ek1f + Ek2f

    could i also use V1i + V1f = V2i + V2f?
  2. jcsd
  3. Jul 24, 2008 #2
    No, you can't say that. If you have [tex]\frac{1}{2}m_1 v_1^2 = \frac{1}{2}m_1 v_{f1}^2 + \frac{1}{2}m_2 v_{f2}^2[/tex] the most you can do is cancel out the 1/2s because there's no way you can cancel out the masses (or the squares).
    You could say [tex]m_1(v_1^2-v_{f1}^2) = m_2v_{f2}^2[/tex]
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