(adsbygoogle = window.adsbygoogle || []).push({}); 1. Here is the question we were given: There are two charges on a horizontal line of 2 m length.

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Qa = +4q Qb = +2q

If a third point of charge "q" is moved between these points, where will the forces acting on it be balanced? Our Professor gave us the answer to be 1.17m to the right of 4q.

2. Coulomb's Law : F = k[Qa][Qb]/(R^2)

k (Coulomb's constant) = 9.0E9

Qa = +4q

Qb = +2q

R = distance between two points (in this case 2 m)

quadratic equation: -b +- sq.root((-b^2 - 4ac)/2a)

3. I know that "q" must be between the Qa and Qb for their forces to cancel (FQa is going to the right, FQb is going to the left.) I also know that you have to set the forces of Qa and Qb to each other. The problem I am having, and this is more basic algebra than anything else I think, is getting it into the quadratic equation to solve for "x" (the distance where "q" is.) I am also not sure what should go in the denominators of either side. This is what I have got so far:

k[Qa][q]/(2-x)^2 = k[Qb][q]/x^2

Getting rid of like terms and such, I get:

(Qa)(x^2) = (4 + 4x + x^2)(Qb)

and plugging in the charges for Qa and Qb:

4x^2 = 8 + 8x + 2x^2, or - 2x^2 + 8x + 8 = 0.

Yet, when I plug this into the quadratic equation, I am certainly not getting the correct answer. What am I doing wrong? Thank you for the help!

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# Homework Help: Finding zero net force between two charges

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