Two insulated balls of mass 0.1 g hang from the same support point by massless insulating threads of length l (as shown in the diagram below.) A total positive charge of 5.70 x 10-07 C is added to the system. Half this charge is taken up by each ball, distributed uniformly, and the balls spread apart to a new equilibrium position. Assuming that the balls hang essentially vertical before the charge is added, what is the tension in each thread before the charge is added? T=-m*g I believe that since the strings are mass less and said to be essentially vertical, then the only equation i should need is Tension=-mass*gravity to get the force of tension on each string. so I have T=-(.1 g)(-9.8 m/s2)=.98 g*m/s2=.98 N but when I enter it onto my course site it tells me I am incorrect. Am i being oblivious to something?