A charge of 35.0 μC is to be split into two parts that are then separated by 5.0 mm.?

Question

A charge of 35.0 μC is to be split into two parts that are then separated by 5.0 mm. What is the maximum possible magnitude of the electrostatic force between those two parts?

Answer 1

F = kq1q2/r^2. (See the ref.) The product of any two numbers summing to a constant is a maximum when the magnitudes of the numbers are equal. That is, (a+ε)*(a-ε) (where |ε| < |a|) = a^2-ε^2 < a^2.

Thus the maximum force occurs when the charges are equal; i.e., 17.5 μC. In that case, F = 9E9*17.5E-6^2/0.005^2 = 110250 N.