# Homework Help: Electric Forces and Coulomb's Law Problem

1. Jan 26, 2012

### Cisneros778

1. The problem statement, all variables and given/known data
In the figure, the net electrostatic force on charge Q2 is zero. If Q1 = -5 nC and Q2 = +7 nC, determine the magnitude of Q0.
http://www.webassign.net/bauerphys1/21-p-079-alt.gif

2. Relevant equations
F = (k*q1*q2)/d^2

3. The attempt at a solution
I notice that Fnetx and Fnety for Q2 are the same.
So I write,
Fq1*cos(theta) + Fq1 sin(theta) - Fq0(.707) = 0
k*q1*q2/d^2*(cos(theta) + sin(theta)) = k*q2*q0/x^2*(.707)
then after some algebra I get,
[q1*x^2*(cos(theta) + sin(theta))]/(d^2*.707) = Q0

I am questioning my method here, but this is what I have done so far.

2. Jan 26, 2012

### Cisneros778

Sorry, d is the distance between q1 and q2
x is the distance between q0 and q2

3. Jan 26, 2012

### Cisneros778

It's funny how when I'm writing how I attempted the solution I get a moment of clarity and I figure out the problem. Thanks anyways, I got it!

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