Question

Two small metallic spheres, each with a mass ofm = 3.00 g, are suspended from a common point by two strings of negligible mass of length L = 62.0 cm. When the spheres have an equal amount of charge, the two strings make an angle of 60° with each other. Calculate the magnitude of the charge on each sphere.

Answer 1

the tension in a string is due to the electrostatic force between the spheres
... and the weight of the sphere

e = w tan(30º) = m * g * tan(30º)

the strings and the separation of the spheres form an equilateral triangle
... so the distance between the spheres is ... 62.0 cm

use the repulsive force and the distance to find the charge