## College Physics (4th Edition)

The magnitude of the force of repulsion is $16 F$
We can find an expression for the original electric force: $F = \frac{k~q_1~q_2}{r^2}$ We can find an expression for the new electric force: $F' = \frac{k~q_1~q_2}{(0.25~r)^2}$ $F' = 16\times \frac{k~q_1~q_2}{r^2}$ $F' = 16~F$ The magnitude of the force of repulsion is $16 F$.