Final answer:
The downward force of 5 N exerted on the book is caused by gravity, not friction, magnetism, or electricity. Gravity is the force that gives weight to objects and depends on their mass and Earth's gravitational acceleration.
Step-by-step explanation:
The downward force of magnitude 5 N exerted on the book is due to the force of gravity. In physics, gravity is the force that attracts objects with mass towards one another. On Earth, gravity gives weight to physical objects and the gravity force experienced by objects is the product of their mass and the acceleration due to gravity (approximately 9.81 m/s² near the Earth's surface).
The force exerted by an object does not depend on its orientation. This force can be calculated using the formula F = ma, where m is the object's mass and a is its acceleration. Since we are considering the force due to gravity, the acceleration a is the acceleration due to gravity.
Other forces such as friction, magnetism, and electricity can also exert forces on objects but are not responsible for the downward force that gives an object its weight.