Three Point Charges, find the electric force exerted

  1. 1. The problem statement, all variables and given/known data
    Three charges, each of magnitude 2 nC, are at separate corners of a square of edge length 1 cm. The two charges at opposite corners are positive, and the other charge is negative. Find the force exerted by these charges on a fourth charge q = +3 nC at the remaining (upper right) corner. (Assume the +x axis is directed to the right and the +y axis is directed upward.)


    2. Relevant equations
    k = (8.988*10^9 N*m^2/C^2)


    3. The attempt at a solution

    Drew a diagram of the problem such that F4 = F1,4 + F2,4 + F 3,4.

    F1,4 = (k*q1*q4)/(r(1,4)^2)j

    F1,4 = (8.988*10^9 N*m^2/C^2)(2.00*10^-9)*((2.00*10^-9)/(0.01m)^2)

    = 3.595 * 10^-4 j

    F2,4 = same

    F3,4 = (k*q1*q2)/(r(2,4)^2)*r(3,4)

    r(3,4) = r(3,1) + r(1,4) = (0.01m)i + (0.01m)j

    r(3,4) = (0.01m)i+(0.01m)j/(sqrt(0.01m^2+0.01m^2)) = 0.14i + 0.14j

    F3,4 = (8.988*10^9) (-2.00*10^-9)(2.00*10^-9)/(0.01sqrt(2)^2)*(0.14i+0.14j)

    = -2.52 * 10 ^ -5

    (3.595 * 10^-4) i - (-2.52*10^-5) i = 3.34*10^-4i <--- Wrong :(
    (3.595 * 10^-4) j - (-2.52*10^-5) j = 3.34*10^-4j <--- Wrong :(


    Any suggestions?? I think that somewhere in computing F3,4 I put in an incorrect number. Thanks!
     
  2. jcsd
  3. TSny

    TSny 6,230
    Homework Helper
    Gold Member

    Check this.
     
  4. Whoa, got .707 now, thanks. So then is everything else correct?
     
  5. TSny

    TSny 6,230
    Homework Helper
    Gold Member

    Did you use the correct value for q4 here?
     
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