A charged polystyrene ball of mass 0.14g is suspended by a nylon thread from a fine glass spring. In the absence of any electric field the spring extends by 30mm. The polystyrene ball is then placed in an electric field that acts vertically upwards, of strength 200kV m^-1, and the spring extends by a further 6mm. What is the electric charge on the ball.
The Attempt at a Solution
change in Ep = Eqd, so 200kV = 200000 Nc^-1 so 200000*q(how di I get q) * 30mm??