The distance $r$ can be calculated using the Pythagorean theorem as the charges are located at the origin and on the $x-y$ plane. The distance $r$ is given by
\[r = \sqrt{(0.3 \, m)^2 + (0.2 \, m)^2} = 0.36 \, m\]
So, $r^2 = (0.36 \, m)^2 = 0.13 \, m^2$.
Show more…