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## Homework Statement

Two spherical point charges each carrying a charge of 40 mC are attached to the two ends of a spring of length 20 cm. If its spring constant is 120 Nm-1, what is the length of the spring when the charges are in equilibrium?

## Homework Equations

1) F = k*(q^2)/r^2 where k is the constant of proportionality

2) F = kx where k is the spring constant

## The Attempt at a Solution

Both equations can be graphed and see where they intersect. I had some trouble getting my calculator to do that, so I set both equations equal to each other and then solved for x.

1) F = 14.4Nm^2/r^2

2) F = 120N/m * r

14.4Nm^2/r^2 = 120N/m * r

x = 0.493242m

Is the logic sound? If you try to solve for r, the forces do not equate.

Thanks in advance!