# Homework Help: Excess electrons question

1. Feb 2, 2008

### ehdubbya

1. The problem statement, all variables and given/known data
My problem states that a pith ball hangs at 20 degrees from the verticle and weighs 3 grams. It is moved 10cm by a charged rod. They both have the same charge. It asks what is the charge on the ball in C and approximatley how many excess electrons are on the ball.

2. Relevant equations
I have the equation kqq/rsquared

3. The attempt at a solution
I found all the sides to the triangle and I do not know where to go from there. I do not know the charges so how can I use the equation with q in it?

2. Feb 2, 2008

### Tom Mattson

Staff Emeritus
10 cm in which direction? x? y? other? And where is the rod in relation to the ball? Is the charge distributed over the entire rod, or is it concentrated at a point?

Did you draw a free-body diagram and set up the equations from Newton's second law? You should have 2 equations in 2 unknowns (q and the tension T in the cord from which the ball hangs).