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Homework Help: Relativity : relativistic energy

  1. Jan 27, 2007 #1
    1. The problem statement, all variables and given/known data
    Find the speed of a particle whose total energy is 3 times its rest energy.

    2. Relevant equations
    [tex]KE = \gamma mc^2 - mc^2[/tex]

    3. The attempt at a solution
    i let total energy = 3mc^2 and then :

    [tex]\gamma mc^2 = KE + mc^2[/tex]
    [tex]3mc^2 = KE + mc^2[/tex]
    [tex]v = \frac{\sqrt{3}}{2} c[/tex]

    Is this correct? or should i let [tex]\gamma mc^2 = 3mc^2[/tex] and work it out immediately?

    Any help will be appreciated.
  2. jcsd
  3. Jan 27, 2007 #2
    [tex]3mc^2 = KE + mc^2[/tex] is correct, but I dont see how is this connected to [tex]v = \frac{\sqrt{3}}{2} c[/tex], So I can't point out which part you did it wrong...
  4. Jan 27, 2007 #3

    Meir Achuz

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    Use 1/sqrt{1-v^2/c^2}=3,and solve for v.
  5. Jan 28, 2007 #4
    yeah, got it thanks, English problem. bah. :P
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