A ball has mass 3.0 µg and charge -7 nC moves from point A to point B. It has the same speed at points A and B

Question

(a) What is the change in electric potential energy of the ball?

(b) What is the change in voltage between points A and B?

Answer 1

I'll bet you haven't told us the whole story. If its mass is given, it's moving vertically against gravity, right? So it has acquired potential energy PE = mg*(B-A). The electric potential energy QΔV must be reduced by an equal amount, so the voltage change is -mg*(B-A)/Q, a positive voltage change.