Charges set on 4 corners of a square

[jbirse]

Homework Statement

Three point charges +Q are placed at three corners of a square, and a charge -Q is placed at the fourth corner. If Q = 1.00 milli-coulomb and the side of the square has length 1.00 m, find the magnitude of net force that the positive charges exert on the negative charge. |F|=

Homework Equations

F = kq1q2/d2
k = 8.99 x 109 N-m2/C2

The Attempt at a Solution

I've tried this problem three times and i only have 2 more attempts to get it right so can anyone help me with this?

 

[diazona]

Sure, we can help you, but show us what work you've done on it first.

 

[Delta2]

You have to use pythagorean theorem to first find the total force F by the 2 charges adjacent to the negative charge. This force F would lie on the same direction as the force from the 3rd positive charge (and that is because the forces from the 2 adjacent charges are both equal in magnitude and vertical to each other) so to find the net force u just add F and the force from the 3rd charge.