1. The problem statement, all variables and given/known data A small sphere with mass .015kg hangs by a thread between two parallel vertical plates .05m apart. The plates are insulating and have a uniform surface charge densities +σ and -σ. The charge on the sphere is q = 8.9 x 10^-6 C. What potential difference between the plates will cause the thread to assume an angle of 30 degrees with the vertical? 2. Relevant equations some formulas in the chapter and on a previous chapter. im not sure which ones are useful: dV = -Edl Ua - Ub = q(Va - Vb) Kb = Ka + Ua - Ub Kb = .5mv^2 Va - Vb = Ed F = qE p = qd Torque = pEsinθ Torque = p X E 3. The attempt at a solution I am clueless. the only thing i know is Ka = 0 because it started at rest. that means Kb/q = Va - Vb but then again the velocity at Kb would = 0 wouldnt it? so I dont know. do I find the F by figuring out E somehow? or does it have something to do with Torque? i dont know how to find p (electric dipole moment). so yea im lost, any help would be appreciated I think it has something to do with the gravity pulling down then the E pulling/pushing to the side.