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Homework Help: KE = p^2/(2m)

  1. Dec 19, 2005 #1
    refer to the title.

    I'm confused whether this eqn works in relativistic situations?

    thanks in advance
  2. jcsd
  3. Dec 19, 2005 #2


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    Staff: Mentor

    No, that equation does not work in relativistic situations. To get the corresponding relativistic equation, take the equations for relativistic kinetic energy and momentum and eliminate v between them:

    [tex]K = \frac{m_0 c^2}{\sqrt{1 - v^2 / c^2}} - m_0 c^2[/tex]

    [tex]p = \frac{m_0 v}{\sqrt{1 - v^2 / c^2}}[/tex]

    Or, you can take the relativistic relationship between total energy, mass and momentum:

    [tex]E^2 = (pc)^2 + (m_0 c^2)^2[/tex]

    substitute [itex]E = m_0 c^2 + K[/itex] (total energy equals rest energy plus kinetic energy), and solve for K.
    Last edited: Dec 19, 2005
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