What is the potential energy of a 3.0kg rock that is 4.0m above the ground?

Two point charges are separated by a certain distance. how does the strength of the electric field produced by the first charge, at the position of the second charge, change if the second charge is doubled? a. the field does not change b. the field strength decreases by half. c. the field strength doubles d. the field strength quadruples

How much work would it take to move a coulomb charge across a 4 volt potential difference?

The electric field inside a cell membrane is 8.0mn/c. what's the force on a singly charged ion in this field?