Final answer:
There is no work done when carrying a book horizontally at a constant height because the displacement in the direction of the gravitational force is zero, and the force and displacement are perpendicular to one another.
Step-by-step explanation:
The question addresses the concept of work in physics, particularly when carrying a book. When you carry a book at a constant height and move horizontally with a constant velocity, no work is done on the book. In physics, work is defined as the product of the force applied to an object and the displacement of the object in the direction of the force. As per the scenario provided, there is no work done when carrying a book because the displacement in the direction of the applied force (gravity) is zero (option b). If you are holding the book and walking, the displacement is horizontal, while the force due to gravity is vertical. Since these two are perpendicular to each other, the angle between the force and displacement is 90 degrees and cos 90º = 0, which makes the work done zero. This is also true regardless of the orientation of the book as the force exerted is always perpendicular to the displacement when carrying the book horizontally.