If an object with charge -3 nC moves from a location that has a potential of -20 V to a location with a potential of -10 V, what has happened to the potential energy of the system?

The potential energy decreases.

Explanation:

Given-

Charge of the object, q = -3nC

Initial potential, Vi = -20V

Final potential, Vf = -10V

Potential energy, U = ?

We know,

Potential, V = U/q

initial potential energy = Viq

                                                        = -20V X -3nC

                                                        = 60 nJ

Final potential energy = Vfq

                                     = -10V X -3nC

                                     = 30nJ

We can see that the potential energy decreases as the object moves from initial to final position which means that the work is done against the electric field.

c. only magnetic

Explanation: