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Mass of an accelerated electron by 31 kV

  1. Jun 8, 2013 #1
    1. The problem statement, all variables and given/known data

    My upper grade teacher in physics has lack of intelligence, and she's not in duty to help people. I would like to clear this out here.

    "An electron is accelerated from rest by the electric tension 31.0 kV. Determine the mass of the electron after the acceleration."

    2. Relevant equations

    I've based my procedure from the principles:

    E = qU

    E = mc^2 - m0c^2

    qU = mc^2 - m0c^2

    m0 = is rest mass --> m0 = 9.1093826*10^-31 kg

    3. The attempt at a solution

    m0c^2 = (9.1093826*10^-31)c^2 --> m0 = 8.18751672*10^-14

    q31000 = mc^2 - 8.18751672*10^-14

    mc^2 = 8.68413672*10^-14

    m = 9.66191907*10^-31 kg

    Is this correct?
  2. jcsd
  3. Jun 8, 2013 #2

    rude man

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    Homework Helper
    Gold Member

    That looks very good, aside from one typo (" m0 = 8.18751672*10^-14 ").

    Be warned that the "modern" way is to let m = rest mass, then your m = (gamma)*m, gamma = 1/[sqrt(1 - (v^2/c^2)]. m0 is no longer used.

    Don't ask me why.
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