How Do You Calculate the Resultant Force on a Charge in an Electric Field?

[thst1003]

Homework Statement

Three charges, q1 = +2.10 10-9 C, q2 = -3.09 10-9 C, and q3 = +1.08 10-9 C, are located on the x-axis at x1 = 0, x2 = 10.0 cm and x3 = 20.0 cm. Find the resultant force on q3.


I am unsure of how to even attempt this problem...

 

[gamma5772]

What is the formula for the force between 2 charged particles? Once you know the force 1 exerts on 3 and the force 2 exerts on 3, it is a simple matter of adding them up -- but remember that force is a vector, so you must use vector addition.