Question

Three charges are arranged as shown in the figure below. Find the magnitude and direction of the electrostatic force on the charge q = 4.74 nC at the origin. (Let r₁₂ = 0.260m.)

magnitude	N
direction

Answer 1

F = k*q1*q/r^2

Calculate the forces and add them up.

q is positive. It is repelled by the +6 nC charge. So the force from that one points in the -x direction (directly away from the +6 nC)

It is attracted to the -3 nC charge. So the force from that one is toward the charge, i.e. in the -y direction.

The forces from these two charges add as perpendicular components. And presumably you know how to find the magnitude and direction of a vector when you have two perpendicular components.