Final answer:
The normal force does zero work on the box as it acts perpendicular to the motion, while the frictional force does negative work. The work done by gravity can be positive depending on the displacement and the angle of the incline.
Step-by-step explanation:
When a box slides down a slope, different forces do work on the object. The work done by the normal force is zero because the normal force acts perpendicular to the displacement of the box. The frictional force does negative work because it opposes the motion, with its magnitude being the product of the frictional force and the displacement along the slope. Finally, the work done by the gravitational force is positive and is calculated as the product of the component of gravitational force along the slope and the displacement.
In your scenario, we might not have the exact displacement or the mass of the box, but generally, the work done by gravity is mg sin(θ) * distance, where θ is the angle of the incline. If the box is sliding at a constant velocity, the work done by friction is equal in magnitude to the work done by gravity but negative, indicating energy is being lost due to friction.