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Homework Help: Electric fields

  1. Sep 23, 2007 #1
    1. The problem statement, all variables and given/known data
    1. The earth has a net electric charge that causes an electric field at its surface equal to 150N/C and directed inward to the center of the Earth.
    (a) What magnitude (and sign) of charge would a 60kg person have to acquire to overcome the weight of the force exerted by the earth's electric field?
    (b) What would be the force of repulsion between two people, each with the charge calculated above and separated by 100m?

    r = 6.37 x 10^6 m
    Me = 5.98 x 10^24 kg
    E = 150 N/C
    Mp = 60 kg
    d = 100m

    2. Relevant equations

    i) E = f/q = (ma)/q

    ii) E = (kq)/r^2

    iii) F = q|E| = (kqq)/d^2

    3. The attempt at a solution

    using eq. i,
    150 = 60(-9.81)/q
    q = -3.924 C

    using eq. iii,
    F = [(9 x 10^9)(-3.924)^2]/(100)^2
    F = 1.39 x 10^7 N
  2. jcsd
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