1. The problem statement, all variables and given/known data What is the distance(d) separating the charged particles dangling on the pendulum? Length of Nonconducting string=120cm mass of particles= 10g Charge q = 1.2*10^-8 2. Relevant equations Fe=(k*q^2)/d^2 3. The attempt at a solution I think I could get this problem easily if I had either the angle between verticle and the nonconducting string or the electric force opposing the masses. I have been using my knowledge of trigonometry to figure this out and trying to manipulate the above equation, but with no luck. Just needed to be pointed in the right direction I think. Thanks!