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## Homework Statement

Two identical small conducting spheres are separated by 0.60 m. The spheres carry different amounts of charges and each sphere experiences an attractive electric force of 10.8 N. The total charge on the two spheres is [itex]=-12\mu C[/itex]. What is the positive charge on one of the spheres?

## Homework Equations

Coulomb's Law.

## The Attempt at a Solution

Part of my problem is I think I am confused about how to treat the signs of the charges.

[tex] q_1 + q_2 = -12 \times 10^{-6} [/tex]

[tex] q_1 = -(q_2 + 12) [/tex]

Coulomb's Law gives:

[tex] 10.8 = k\frac{q_2(q2_+12)}{0.60^2} [/tex]

I left out the negative sign, because of the absolute value in Coulomb's law.

Is this correct?

and leads me to

[tex] 0 = q_2^2 + (12\times 10^{-6})q_2 - 4.32601 \times 10^{-10} [/tex]

From this, I end up with two solutions that fit the conditions of the problem. Is that right? I get a positive root of 27.6 micro C, and a negative root of 15.6 micro C, which gives me the positive charge of 3.6 micro C.

Could anyone confirm that this is the right way to handle this situation, or clear up my sign confusion for me?

Thanks so much,

Sheldon

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