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Help with relativity problem

  1. Apr 2, 2007 #1
    How close would two stationary electrons have to be positioned so that their total mass is 7 times what it is when the electrons are very far apart?

    Here's my setup:

    2mC^2 is the energy of the 2 electrons when they're far apart.
    2mC^2 + kqq/r^2 is the energy of the 2 electrons when they're close.
    Since the mass is 7 times the far apart mass:

    14mC^2= 2mC^2 + kqq/r^2

    m = mass of electron = 9.11e-31
    k = 8.99e9
    q = 1.6e-19
    C = 3e8

    at the end I got r = 1.53e-8 meters.... but that's wrong...
    can anyone tell me where I messed up?

  2. jcsd
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