# Find the Coulomb force between two electric charges of 4 xx 10^(-6) C and 5 xx 10^(-6) C, if the distance between the two charges is 2 cm?

First we need to convert the distance to the SI unit, so it is $0.02$ $m$.
Then $F = \frac{k {q}_{1} {q}_{2}}{r} ^ 2 = \frac{9 \times {10}^{9} \times 4 \times {10}^{- 6} \times 5 \times {10}^{- 6}}{0.02} = 9$ $N$