a ball with a mass of 0.150 g and positive charge of q=41.2 C is suspended on a string of negligible mass in a uniform electric field. We observe that the ball hangs at an angle of =22.0o from the vertical. What is the magnitude of the electric field?

Answer 1

force down on ball = m g
m = .15*10^-3 = 1.5*10^-4 kg
g = 9.81

I assume E is horizontal ?

Force sideways on ball = q E

tan 22 = qE / mg