Final answer:
The electric potential energy of a -3.00 nC charge cannot be determined without additional information about the system it is in. For a known system of point charges, the electric potential energy can be calculated using Coulomb's Law for each pair of charges and summing these values.
Step-by-step explanation:
The student asked about the electric potential energy of a -3.00 nC charge. To answer this, we would need more information such as the positions of other charges in the system and distances between them, because the electric potential energy of a charge in a system depends on its position relative to other charges and their magnitudes. Without additional context, the electric potential energy cannot be determined solely based on the charge value given.
However, in a system of point charges, like the one described with a 1.00 µC charge at the origin, a -2.00 µC charge at x=30 cm, and a 3.00 µC charge at x=70 cm, the total potential energy of the configuration can be calculated using Coulomb's Law to determine the potential energy between each pair of charges and summing those values. This involves calculating the potential energy for each pair of charges: between the 1.00 µC and -2.00 µC charges, between the -2.00 µC and 3.00 µC charges, and between the 1.00 µC and 3.00 µC charges. Changes in the system, like swapping the positions of the -2.00 µC and 3.00 µC charges, will affect the total potential energy, as the distances between charges alter, and therefore, the pairwise potential energy values change.