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Homework Help: Magnitude of an electric force problem with vectors

  1. Apr 30, 2007 #1
    1. The problem statement, all variables and given/known data
    Two equal positive charges, both q = 2.0 x 10^ -6 C, interact with a third charge Q = 4.0 x 10^ -6 C, as shown above. What is the magnitude of the electric force on Q?[/B][/B]

    2. Relevant equations
    Electric force = Kc (q1/r^2)

    3. The attempt at a solution
    Basically, I believe that my problem is in solving the vectors.
    I attempted to break down the charges(it is hard to show this work on here but...) I broke it down into....
    E(y) = E(1) x sin Θ(1) + E(2) x sin Θ(2)
    E(x) = E(1) x cox Θ(1) - E(2) sin Θ(2)
    I'm not sure if that makes sense, but it was all I could think of...Any help would be greatly appreciated. Thanks a lot!

    Attached Files:

    • scan.jpg
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  2. jcsd
  3. Apr 30, 2007 #2

    Chi Meson

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    I'm sure you meant "cos", not "sin" there right?

    While waiting for the image, it sounds like your reasoning is correct. You are summing the x and y componants of the separate forces on the thrid charge. Next you need to determine the net force.

    Hey, how did you type those thetas in there?
    Last edited: Apr 30, 2007
  4. Apr 30, 2007 #3
    thanks chi,
    so i believe my second set should actually look like...
    E(x) = E(1) x cosx Θ(1) - E(2) cos Θ(2)
    then once i plug in my values and simplify, i should get my x component any my y component, right? then i just use the pythagorean theorem to solve?

    oh, and for the thetas i just happened to come across one on a wensite and i copied and pasted. .
  5. Apr 30, 2007 #4

    Chi Meson

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    wow, must be some ASCII trick.

    Anyway, now that I see the drawing, please notice that the two vertical componants are balancing out while the two horizontal componants are working together. Simpler now, isn't it?
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