[SOLVED] Electric Charge 1. The problem statement, all variables and given/known data Two point charges q and 4 q are distance L apart and free to move. A third charge is placed so that the entire three-charge system is in static equilibrium. What is the magnitude of the third charge? 2. Relevant equations F = kq1q2 / r^2 k ~= 8.988x10^9 3. The attempt at a solution Not a clue. All I've figured out is that for this to work in perfect equilibrium, the third charge must be directly in between the first two. Not looking for an all-out solution from anyone (Although that'd be cool too), but more looking for just a push in the right direction. In theory, it'd involve drawing free body diagrams for the three charges, and then working with the charge q3 to balance the equilibrium... but I can't grasp my head around that.