Just a Hint on How to Do This Question?

[Procrastinate]

Two small spheres, each of mass 5.0g, are each supported from the same point by a light insulating thread 500mm long. When they are given equal charges they repel each other so that the distance between them is 80mm. Find the charge on each.

I don't want any worked solutions or anything, so I doubt I'll need the template. However, I just want a hint as to how to go about this question? It's meant to be a problem solving question but I'm not sure what to do with the masses of the spheres.

And the only relevant equation here is Coulomb's Law so any other hints that deviate from this probably wouldn't help me.

 

[jtbell]

And the only relevant equation here is Coulomb's Law

Are you sure gravity isn't involved in this somehow?

 

[whybother]

You know that the distance given, 80mm, must be an equilibrium point for the system, so you basically just need to balance the forces -- the possible forces here are gravity, tension from the string, and, of course, the electrostatic repulsion - just draw a force diagram.