(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A ball, which we can treat as a point charge, has a charge of +Q and a weight of 9.00 N. This ball is 50 cm away from a ball of charge -10Q, which is fixed in position. The +Q ball is 30 cm vertically below, and 40 cm horizontally, from the other ball, and the +Q ball is held in equilibrium at that position by a string which happens to be perfectly horizontal

Image: http://www.webassign.net/userimages/81225?db=v4net

1) What is the magnitude of the electrostatic force that the ball with the charge of -10Q exerts on the ball with the charge of +Q?

2) What is the magnitude of the tension in the string?

3) What is the value of Q?

2. Relevant equations

Fn = mgcos0

Fe = k(q1)(q2)/r^2

Fw = mg

3. The attempt at a solution

I know this problem needs to be broken down into components, so I started off trying to figure out how to break up the Forces by drawing a free body diagram. On the -10Q ball there is Fn pointing upwards and mg directed downwards correct? To get the diagonal force I have to use mgcos0 which becomes mg(30/50)...I do not know if this is correct because I am trying to sum up all the forces in the x direction and all the forces in the y direction. As for finding the tension, I know it involves the same kind of process but I am confused on where to start since I think I need the answer to 1). with that answer I will be able to find answer 3 using coulomb's law.

Thanks for all the help!

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# Homework Help: Coulumb's Law and force between charge

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