Final answer:
The gravitational potential energy of the object increases by 15 joules, which is the work done to lift the object from 3 m to 8 m above the ground assuming no non-conservative forces are at work (like friction) or changes in kinetic energy.
Step-by-step explanation:
The student has asked what the change in the gravitational potential energy of an object is when it is lifted from 3 m above the ground to 8 m above the ground, with 15 joules of work done by forces other than gravity.
The gravitational potential energy (PEg) of an object increases when it is lifted to a greater height, as the formula PEg = mgh indicates. Here, 'm' is mass, 'g' is the acceleration due to gravity, and 'h' is the height above the reference point. To calculate the change in gravitational potential energy, we multiply the mass (which remains constant) by 'g' (which is also constant near the Earth's surface) and by the change in height.
In this case, the change in height (∆h) is 8 m - 3 m = 5 m. Therefore, the change in gravitational potential energy (if we ignore any change in kinetic energy) is equal to the work done against gravity. This is because the work done by forces other than gravity does not change the gravitational potential energy. So the increase in gravitational potential energy is:
∆PEg = m × g × ∆h
Since the mass and gravity are not given, but we know the work done by forces other than gravity is 15 joules, we cannot directly calculate the change using the formula. However, we can infer that the change in gravitational potential energy is the same as the work done against gravity to lift the object the extra 5 meters, assuming no energy losses to non-conservative forces (like friction) or gains in kinetic energy.
Hence, the answer is:
The change in gravitational potential energy of the object increases by 15 joules (Option D).