A 3.5-gram ping-pong ball with charge q is hanging static from an infinite plane of charge, using a nonconducting 25−cm long massless string, as shown below. The angle of the string with the plane is 20 degree, and plane itself makes angle of 30 degree with horizontal. What is the magnitude of the charge q if the surface charge density of the infinite plane of charge is 16 μC/m2? Hint: Draw the free-body diagram of the ping-pong ball.
