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Homework Help: Coulombs Law is KILLING ME! please help

  1. May 7, 2008 #1
    1. The problem statement, all variables and given/known data

    You remove two socks from a hot dryer and find that they repel with force of 0.002 N when they’re 1 cm apart. If they have equal charges, and you separate the socks until they’re 5 cm apart, what force will each sock exert on the other? Round the answer to 3 significant digits.

    2. Relevant equations

    F=8.9*10^9(q1)(q2) / r^2

    3. The attempt at a solution

    Ive been working on this for over an hour and am frieking out! First I try to solve for the two charges, using .1 (1cm-converted to meter). I know that once I get this, I can use it to change .1 to .5 and solve for F. Problem is I have been having trouble solving for Q!!! which leaves me stuck in the begining.

    Please please help, Ive got a midterm in the morning.:confused:
     
  2. jcsd
  3. May 8, 2008 #2
    F=kq1q2/r^2

    at .01m, F = .002
    Solve for q^2, since q1 = q2
    q^2= (0.002)(.01^2) / (8.9e+9)
    = 2.25e-17 C
    so q1 or q2 equals the square root of q^2:
    (2.25e-17)^0.5 = 4.74e-9 C

    Then, use these values to solve if r = .05 (just plug them back into the equation)

    I hope this helped
     
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