Electromagnetic force and some trig

[bobsmith76]

Homework Statement

The diagram below shows two pith balls, equally charged and each with a mass of 1.5 g. While one ball is suspended by a thread, the other is brought close to it and a state of equi- librium is reached. In that situation, the two balls are separated by 2.6 cm and the thread attached to the suspended ball makes an angle of 20 ̊ with the vertical. Calculate the charge on each of the pith balls.

Homework Equations

N = (k(C₁C₂)/r²

where k = 9 * 10⁹

The Attempt at a Solution

My problem here is that I'm dealing with unknowns on both sides of the equation. I have to find out N and x.

N = (9*10^9(x^2))/1.3^2

I don't know why they give us the information that the angle is 20 degrees. In any case I figured out the dimensions of the triangle which are

7.2, 2.6, 7.65

but I can't figure out how that helps me.

 

[SammyS]

Force is a vector quantity.

There are three forces involved.

Break the forces down into horizontal and vertical components. (That's why you need to know the angle.)