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I was training with some example exams, and I found out a problem that I don't know how to start with it, not even a main formula...

Two balls with masses of 0.5g each hang on threads 0.8m long each tied to a common hook.

What charge has been acquired by the system if, as a result, an angle 2α=15º has been established between the threads?

Well, this is the maximum point I have reached... and I don't know if this actually have any relation with the exercise:

Someone can tell me how to start?

Thank you very much in advance...

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Hi Anne - you seem to have your set up correctly. Try drawing a free body diagram and consider the different forces involved. Also, there is a simple expression for the force between two charged bodies that should help clear it up. – Jen Jan 2 '12 at 6:10
FBD will solve your problem, use the angle for deducing the angle between forces. – Vineet Menon Jan 2 '12 at 6:39
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Hi Anne, and welcome to Physics Stack Exchange! This is not really a homework help site; it's for conceptual questions about physics. Accordingly, if you'd like to ask a homework problem, we expect you to narrow it down to the specific physics concept that is giving you trouble. Just asking "how do I start?" doesn't tell us what you're confused about, or how we can best help you. If you can edit this question to focus on a specific concept, I'll be happy to reopen it. See our homework FAQ for more information. – David Zaslavsky♦ Jan 2 '12 at 7:08

closed as too localized by David Zaslavsky♦ Jan 2 '12 at 7:04

This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. For help making this question more broadly applicable, see the FAQ.