1. The problem statement, all variables and given/known dataObject A has mass 90.0 g and hangs from an insulated thread. When object B, which has a charge of +130 nC, is held nearby, A is attracted to it. In equilibrium, A hangs at an angle θ = 7.20° with respect to the vertical and is 5.00 cm to the left of B. (a) What is the charge on A? (b) What is the tension in the thread? http://i694.photobucket.com/albums/vv301/redraven45/physics1_zps6759b55e.png 2. Relevant equations F = ma F = kq1q2/r^2 3. The attempt at a solution Im pretty clueless on this one. I know it's some type of equilibrium question, and it looks like the forces on the x direction cancel out. To find the charge on A, I need the force between the two charges but I don't have that and I'm not sure if I'm doing this right. The only force on the string in the y direction is from gravity so Fy = 0.09*9.8 =0.882N The only force pulling the string in the x direction is the force between charge A and charge B tantheta = Fx/Fy Fx = tantheta*Fy = tan7.2*0.882 = 1.15N This equals to the force between the two charges, so 1.15 = k(qA)(qB)/(r^2) (qA) = 1.15 *0.05^2/ (8.85e-12)(130e-9) (qA) = 2.49e15 this value doesn't make much sense. not sure what to do.