Charges...please help!! 1. The problem statement, all variables and given/known data Two 3.52 g point charges on 7.49-m-long threads repel each other after being equally charged. What is the charge q? (θ=31°.) 2. Relevant equations F = KQQ/R^2 3. The attempt at a solution How do I find Q without having a distance r???
Oh yea...so the length from the center to one of the masses is 3.858 m. So I can do... F = K*Q*Q/r^2 F = K*Q^2/ r^2 An wouldn't F = 0 since they cancel each other out?
That's one force. List them all. (And draw yourself a free body diagram showing how the force act on each mass.)
Yes, but realize that forces are vectors--direction counts. Set up two equations: One for the horizontal components, one for the vertical components. Combine these to solve for the charge.
I'd write that first equation as: Tsinθ - qE = 0 (since the force components are in opposite directions) Realize that E is also a function of q, so rewrite that in terms of k, q, and r (which you figured out). Otherwise, you are on the right track.
Okay so I end up with... -q = -(mg*tanθ) / (kq/r^2) q = (mg*tanθ) / (kq/r^2) and the q's cancel? = (mg*tanθ) / (k/r^2)