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Homework Help: Modern Physics relativistic

  1. Mar 10, 2005 #1
    How much mass does an electron gain if it is accelerated to an energy of 500 MeV?

    My solution:

    I am using the mass of the electron in terms of "energy units"... that is
    m_e = 0.511 MeV/c^2 where c is the speed of light.

    The total energy is E = Eo + ke, where ke is kinetic energy

    Am I right here... mc^2 = m_ec^2 + ke?

    I mean.. should my E be mc^2/(1 - v^2/c^2)^(1/2)? I am confused.. but
    if I were to use that "relativistic" formula, I am not given the value of v.

    Then m = m_e + ke/c^2.

    Let m_e = 0.511 MeV/c^2 and ke = 500MeV

    m = 500.511 MeV/c^2

    Converting this mass to kilograms results to m = 8.9 x 10^-28 kg.
  2. jcsd
  3. Mar 10, 2005 #2
    is correct

    THis is right if that m is the rest mass of the electron/particle.

    [tex] E = \gamma m_0 c^2 [/tex]
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