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Homework Help: Electrostatic Forces of an Equilateral Triangle

  1. Apr 4, 2012 #1
    1. The problem statement, all variables and given/known data
    Three point charges are located at the corners of an equilateral triangle as in the figure below. calculate the net electric force on the 7-nc charge.

    Each sides are .5 m. (q1=7μc) (q2=2 μc) (q3= -4 μc)
    ___1
    __/__\
    2/____\3




    2. Relevant equations
    f=k q1 q2 / r^2


    3. The attempt at a solution
    F12= 8.988x10^9 (7x10^-6)(2x10^-6) /.5^2= 0.5
    F13=8.988x10^9 (7x10^-6)(4x10^-6) / .5^2 = 1.006656

    X
    F12x=.5cos60=.25
    F13x=1.006656cos-60=.503328
    Rx=.25+.503328= .753328

    Y
    F12y=.5sin60= (sqrt of 3)/4=.4330127019
    F13y=1.006656cos-60=-.4358948344
    Ry=-2.882132598x10^-3

    sqrt of (.753328^2+(-2.883132508x10^-3)^2)=.7534N
    tan-1(-2.88...x10^-3 / .753328)= -.22°

    I don't know what i'm doing wrong, but the answers i'm gettin aren't correct. help. thanks!:confused:
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Apr 4, 2012 #2
    would the angle between the two forces be 60 degrees??
     
  4. Apr 4, 2012 #3
    and why dont you directly find thier vector sum? why break it into components?
     
  5. Apr 8, 2012 #4
    yes it's equilateral
     
  6. Apr 8, 2012 #5
    the angle b/w the two forces on q=7 is 120 degrees
    then
    Fnet^2 = F1^2 +F2^2 -2*1/2 *F1*F2
    Fnet = 15.06 (around)
     
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