Question
A ping-pong ball has been electrostatically charged such that it has 2.5 x 1015 excess electrons. The ball has a massof 1.0 g. It is observed to float motionless in the presence of auniform electric field. What is the magnitude and direction of this electric field.
Hint: The ping-pong balls weight = mg is adownward force. g is the acceleration due to gravity = 9.8m/s2.