Question

Long, long ago, on a planet far, far away, a physics experiment was carried out. First, a 0.250-kg ball with zero net charge was dropped from rest at a height of 1.00 m. The ball landed 0.400 s later. Next, the ball was given a net charge of 7.80 μC and dropped in the same way from the same height. This time the ball fell for 0.640 s before landing.

What is the electric potential at a height of 1.00 m above the ground on this planet, given that the electric potential at ground level is zero? (Air resistance can be ignored.)

Answer 1

When there was no charge then only gravitational acceleration was acting. Let the value of gravitational acceleration is then

Now when the charge is given then it will accelerate due to both gravity and electrostatic field. Let the acceleration due to electrostatic field is then

Since the sign of come out to be negative with respect to hence, it will act in the upward direction.

Also

Since the field is in upward direction hence potential at the height will have lower value than zero hence