Question

A point charge of +3.5 μC is placed 0.800 m to the left of the second, identical point charge.

What is the magnitudes and directions of forces that each charge exerts on the other?

Answer 1

Two identical point charges will have the equal magnitudes of forces that each charge exerts on the other:

$$F_{12}=F_{21}=\dfrac{kq_1q_2}{r^2},$$ $$F_{12}=F_{21}=\dfrac{9.0\times10^9\ \dfrac{N\times m^2}{C^2}\times(3.5\times10^{-6}\ C)^2}{(0.8\ m)^2},$$ $$F_{12}=F_{21}=0.17\ N.$$

Since two charges are both positively charged they will repel each other. As a result, the force on charge $q_1$ is opposite in direction to the force it exerts on charge $q_2$.