# Homework Help: Magnitude of an electric force problem with vectors

1. Apr 30, 2007

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!

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2. Apr 30, 2007

### Chi Meson

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
3. Apr 30, 2007

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. .

4. Apr 30, 2007

### Chi Meson

Θ

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?