Question

A force 1500N exists between two identical point charges separated by a distance of 30cm. Calculate the magnitude of the two point charges.

Answer 1

$$F=k\frac{q_1q_2}{r^2}=k\frac{q^2}{r^2}$$

$$q=\sqrt{Fr^2/k}\\ =\sqrt{1500*0.3^2/9*10^9}=1.2*10^{-4}\:\rm C$$