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1MileCrash

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## Homework Statement

Two identical conducting spheres, fixed in place, attract each other with a force of 0.111 N when their center to center separation is 45.00 cm. The spheres are then connected by a thin conducting wire. When the wire is removed, the spheres have a net positive charge and repel each other with an electrostatic force of 0.043 N. What was the initial negative charge on one of the spheres, and what was the initial positive charge on the other?

## Homework Equations

Coulomb's Law

## The Attempt at a Solution

I posted a problem nearly EXACTLY like this and I still don't understand.

First, since they are attracting initially I know they have opposite signs. To be mathematically consistent, I will then call this force in the negative direction.

[itex]-.111 = kq_{1}q_{2}r^{-2}[/itex]

I also know that after being connected, both spheres have a charge of

[itex]q_{f} = 0.5(q_{1} + q_{2})[/itex]

So then I can use Coulomb's Law with the final force,

[itex]0.43 = kq^{2}_{f}r^{-2}[/itex]

Which allows me to solve for that final charge.

[itex]9.84x10^{-8} = q_{f}[/itex]

Then I can use this numerical value to solve for one of the initial forces.

[itex]1.96x10^{-7} - q_{1} = q_{2}[/itex]

Then I can substitute this into the initial force equation for a quadratic.

[itex]0 = 1.96x10^{-7}q_{1} - q^{2}_{1} + 2.5x10^{-14}[/itex]

Then I can use the quadratic formula to get the two solutions,

-8.8x10^-8, and 2.84x10^-7.

Then I can hit submit to waste one of my attempts because I am doing it wrong.