Final answer:
The work done by the normal force on a box sliding across a flat floor is zero, due to the perpendicular orientation of the force with respect to the displacement.
Step-by-step explanation:
The work done by the normal force on a box sliding across a flat floor is zero. This is because work is defined as the force applied over a distance where the force and the displacement must have a component along the same direction. The normal force acts perpendicular to the displacement (which is horizontal), meaning that there is no component of the normal force in the direction of displacement.
In the given problem, even though the normal force is equal to the weight of the box (due to gravity), which would be 27 kg × 9.8 m/s2 (assuming standard Earth gravity), and the box moves 6 meters to the left, the work done by the normal force remains zero because the displacement is purely horizontal while the normal force is vertical.