Question

Two charges are located on the positive x-axis of a coordinate system. Charge 𝑞₁ = 2 × 10⁻⁹𝐶 is 2cm from the origin, and charge 𝑞₂ = −3 × 10⁻⁹𝐶 is 4cm from the origin. What is the total force exerted by these two charges on a charge 𝑞₃ = 5 × 10⁻⁹𝐶 located at the origin?

Answer 1

The net force

$$F=-F_{23}+F_{13}=-k\frac{|q_2||q_3|}{r_{23}^2}+k\frac{|q_1||q_3|}{r_{13}^2}$$

$$F=-9\times 10^9\times \frac{3\times 10^{-9}\times 5\times 10^{-9}} {0.04^2}\\ +9\times 10^9\times \frac{2\times 10^{-9}\times 5\times 10^{-9}} {0.02^2}=1.4\times 10^{-4}\:\rm N$$