If you increase the distance between two identical point charges so that the new distance is five times the original distance, what happens to the force between them?

Question

I know it is suppose to be divided by 25 but why?

Answer 1

Coulomb's Law

F1=k•q1•q2/r²
F2=k•q1•q2/R²
If R=5r, then F2=F1/25

Answer 2

It's called an inverse square law.
Gravity of a point mass behaves the same way.