Question

Find the distance of two charges with q₁ = 94 nC and q₂ = 45 μC, the force of the 2 charges is 0.81 N

Answer 1

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

$$r=\sqrt{\frac{kq_1q_2}{F}}\\ =\sqrt{\frac{9*10^9*94*10^{-9}*45*10^{-6}}{0.81}}=0.22\:\rm m=22\: cm$$