How Do You Calculate the Charge and Number of Excess Electrons on a Pith Ball?

[ehdubbya]

Homework Statement

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.

Homework Equations

I have the equation kqq/rsquared

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?

 

[quantumdude]

It is moved 10cm by a charged rod.

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?

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?

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).