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Homework Help: Electric charges, wrong answer D: ?

  1. Jul 27, 2011 #1
    1. The problem statement, all variables and given/known data

    Find the net force at point A

    q1=-6x10^-5 C
    q2=-3x10^-5 C

    q1 is 3m north of A
    q2 is 3m east of A

    find the net force on a -1.2x10^-5 C charge

    3. The attempt at a solution

    first off I find how the electric field is with no charge at point A

    = 6.7 x 10^4 N/C [E 63 degrees N]

    = Fe= qE
    Fe= (-1.2x10^-5)(6.7x10^4)
    Fe= 0.804 [W 63 degrees S]

    However the answer in the book says the answer is 8x10^4 N [W63degreesS]

    i dont know if it is me or the book making the mistake?
  2. jcsd
  3. Jul 27, 2011 #2


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    Homework Helper

    Read carefully to make sure the distances really are 3m. That is a long way away.
    Your calculation look OK to me, given the figures you have provided here. But to 3 figures that should be 0.805 [0.804984]
    Given that some of the data was given to only 1 significant figure - you answer should have been 0.8

    Last edited: Jul 27, 2011
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