## College Physics (4th Edition)

The work done by an external agent is $2.3\times 10^{-13}~J$
We can find the electric potential energy: $U = \frac{k~q_1~q_2}{r}$ $U = \frac{(9.0\times 10^9~N~m^2/C^2)(1.6\times 10^{-19}~C)(1.6\times 10^{-19}~C)}{1.0\times 10^{-15}~m}$ $U = 2.3\times 10^{-13}~J$ When the charges are at an infinite separation, the electric potential energy is zero. Therefore, the work done by an external agent is $2.3\times 10^{-13}~J$