# Electrostatic forces helpp

1. Jan 14, 2009

### krnaudio

Electrostatic forces helpp!!

1. The problem statement, all variables and given/known data
Two spheres, each having a mass of 50.0 mg, are suspended from a common point by massless threads 50.0 cm long. One of the spheres have been given a charge twice that of the other. The strings make an angle of 6.00 degrees.
What are the charges on each of the spheres?

2. Relevant equations
F = k ((q1)(q2))/r^2

3. The attempt at a solution

Since the lengths of the strings on both sides are 50 cm, I drew an imaginary line between the two spheres. I found out that the other two angles had to be 87 degrees because both of the sides were equal. Then, I used law of cosines to find that the length between the spheres is 27.4 cm, which would be r in the equation. I also know that either q1 = 2q2 or q2 = 2q1, but I do not understand how I am supposed to use the masses of the spheres to find out the charge. Is there an equation that I'm missing here??

2. Jan 14, 2009

### tiny-tim

Welcome to PF!

Hi krnaudio ! Welcome to PF!

There are three forces on each sphere … tension, gravity, and electric …

so make the vector sum zero (or draw a vector triangle )