posted by Steve .
Charge q1 = 6 uC is at the origin, charge q2 = 7 uC is at y = 2m, x = 0, charge q3 = 1.5 uC is at y = -1 m, x = 0. What is the force on q2?
Add the forces due to q1 and q3. All charges are located along the x axis.
q1 pushes q2 to the left, and q3 pushes q2 to the right. Therefore you will have to subtract one force from the other to get the difference. Both are forces of repulsion, since all charges are the same.
To compute the force of one particle on another, use Coulomb's law.
F = k q q'/R^2