Finding Electric Forces Between Identical Spheres

[batman1169200]

Homework Statement

Two identical conducting small spheres are placed with their centers 0.300m apart. One is given a charge of 12.0 nC and the other a charge of -18.0 nC. a) Find the electric force exerted by one sphere on the other. b) Next, the spheres are connected by a conducting wire. Find the electric force between the two after they have come to equilibrium.

Homework Equations

F_e = (k_e)*(q1*q2)/(r^2)

The Attempt at a Solution

k_e is a constant of 8.99e9 N*m^2/C^2
plug the rest but I just don't understand the signs that well. Also when do i use the directional equation.

 

[kkrizka]

For the signs, I suggest you think about what direction forces have depending on their charges instead of trying to to plug them into the equation.