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Homework Help: I need some guidance on my coulomb's law homework.

  1. Sep 9, 2012 #1
    1. The problem statement, all variables and given/known data
    two charged particles held fixed in the xy plane are: q1= +3.0 μC, x1=3.5 cm, y1= 0.50 cm, and q2= -4.0 μC, x2= -2.0 cm, y2= 1.5 cm.

    (question 1) What is the magnitude and the direction of the electrostatic force on q2. ?

    (question 2) Where would a third charge q3= +4 μC be placed so that the net electrostatic force on q2 is zero?

    2. Relevant equations
    For question one i came out to 0.025N @144° ccw
    is that even remotely correct?

    3. The attempt at a solution
    I don't want the answer, i would like to just know the steps so that i can try it for myself.
    Ive added the x's amd y's and came out with

    Ʃ x= 0.035-0.02= 0.015
    Ʃ y= 0.005+0.015=.02

    from here what can i do ?
    could i just inverse the angle from q2 to find the position?
  2. jcsd
  3. Sep 10, 2012 #2


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    Gold Member

    Can you show your working for how you get 0.025N at 144o counterclockwise?
  4. Sep 10, 2012 #3


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    Staff Emeritus
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    Why are you adding the x coordinates and adding the y coordinates ?

    The distance between points, (x1, y1) and (x2, y2) is [itex]d=\sqrt{(x_2-x_1)^2+(y_2-y_1)^2}\ .[/itex]
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