Question

A small m = 2.00 g plastic ball is suspended by a L = 24.0 cm long string in a uniform electric field, as shown in Figure P15.50. If the ball is in equilibrium when the string makes a 18.0° angle with the vertical as indicated, what is the net charge on the ball?

Answer 1

To slove as listed, you need to know the charge of the Electric Field:

Fx=Fy
Eqsin(18)= mgcos(18)

q=mgcos(18)/ Esin(18)

since cos/sin= tan

q= mg tan(18)/E