# Coulomb's law charge

1. Feb 19, 2010

### dom192

1. The problem statement, all variables and given/known data
two pith balls are suspended on a wooden dowel and have the same origin point. the two balls are push away from each other and are equally negatively charge. the string have the lenght L and the two strings form angle (theta).

knowing

Fg= Gm1m2/r^2

Fe= kq1q2/r^2

2. Relevant equations
using the electrostatic constant k dervie the formula below.

Q= 2Lsin(theta) x square root of [mgtan(theta)/k]

3. The attempt at a solution

i found out that Fe= mgtan(theta) and Fe -Ft is the horizontal component. then i dont know wat to do after.

2. Feb 21, 2010

### dr_k

Good Afternoon dom192,

This is a statics problem. You need to draw a precise picture of the problem, then isolate one of the pith balls, and apply Newton's 2nd postulate for static equilibrium,
Fnet = 0. These two equations will then allow you to solve for the unknown Q.

To get you started, here's a picture:

http://img109.imageshack.us/img109/6382/estatics1.jpg [Broken]

Last edited by a moderator: May 4, 2017