Electric Forces between charges

[thst1003]

1.

Hanging from threads are two charged balls made of pith (a very light, spongy material that comes from inside the stems of certain plants). The balls each have a mass of 0.100 g and a charge of the same magnitude q and are attracted toward each other, as shown in the figure below. (Take θ = 18.9° and r = 1.82 cm.)

Question: What is the magnitude of the electric force?


F = k (q x q/r^2)

Please Help. I could not figure out how to solve without q.

 

[cupid.callin]

use the equilibrium for on charge ...

ie .. vertical component of tension balances weight and horizontal balances electric force

you'll get charge ...