1. The problem statement, all variables and given/known data 2 small spheres each having a mass of 0.1g are suspended from the same point on silk threads 20cm long. When given equal charges, they repel, resting 24cm apart. Calculate charge of each. 2. Relevant equations F(w)=mg(a) F=kQ(1)Q(2)/d^2 k=8.987x10^9 N*m^2 / c^2 3. The attempt at a solution I converted grams to kilograms.. 1 x 10^-4 kg kilograms to newtons/weight..9.8*10^-4N blah blah.. F=kQ(1)Q(2)/d^2 (7.35*10^-4N)(.24^2)(8.987*10^9 N*m^2/c^2)=Q^2 Q=6.86*10^-8C http://i80.photobucket.com/albums/j199/pugfug90/physucks.gif [Broken] Here's some work and a diagram. I am 99% sure that the answer is 6.9*10^-8 coulombs. However! I don't understand.. If I used trig to find half of the total force (in the triangle diagram).. why do I use the full distance?