A ping-pong ball covered with a conducting graphite coating has a mass of 5.0  103 kg and a charge of 4.0 µC

Question

A ping-pong ball covered with a conducting graphite coating has a mass of 5.0  103 kg and a charge of 4.0 µC. What electric field directed upward will exactly balance the weight of the ball? (g = 9.8 m/s2)

Answer 1

The weight mg will try to move downwards and force (electical) exerted by the field will try lifting it upwards

If the balance is balanced in air the

q E = mg

mass m = 5*10^-3 kg (5 miligram) what it should be like for such games.

E = mg / q = 5*10^-3*9.8/4*10^-6 = N/Quolomb
= 12250 N/Quolomb upwards