# Estimating charges coulomb's law

1. Jan 28, 2008

### mussgo

this is my first time posting here in the forums right now im really stuck with this problem
i already tried solving it on my own but i can't i will really apreciate any feedback or hint i could use to solve it U_U

Estimating Charge Two hard rubber spheres of mass ~20 g are rubbed vigorously with fur on a dry day. They are then suspended from a rod with two insulating strings of length 10 cm. They are observed to hang at equilibrium, 19° from vertical, as shown in Fig. 22-41. Estimate the amount of charge that is found on each sphere

3. The attempt at a solution i saw a somewhat similar problem on my text and i tried ths equation

x= (2*k*L*q^2 / mg )^1/3

where L is the length of the cord and x the separation of the balls and my final answer was wrong :S did i use the right equation :S???

Last edited: Jan 28, 2008
2. Jan 29, 2008

### Shooting Star

Completely wrong.

The description of the problem is incomplete. (There is no figure.) Are the strings tied to the rod at the same point? If not, what is the separation?

In any case, there are three forces acting on a ball to keeep it in equilibrium. Can you draw a freebody diagram of that? Then you can split the forces into horz and vert dircns.

Do you know the force between two charges?