A small plastic sphere with a charge of - 6.0 nC is near another small plastic sphere with a charge of - 14 nC. If the spheres repel one another with a force of magnitude 8.3*10-4 N, what is the distance between the spheres?

Here is how to answer the question.

Use the formula:

F = kq1q2/r^2

F = force = 8.3x10^-4N

q1, q2 = charges

r = separatioon

k = constant = 9x10^9 in MKS units

so we have

r = sqrt[k q1 q2/F]

r = sqrt[9x10^9 * (-14) x10^-9 * (-6) x10^-9 / 8.3x10^-4 ]

r = 0.0302 m

So the distance between spheres is 0.0302 m