Question

A book is pushed across the table by a student. The student stops pushing on the book and the book slows down and stops. The force stopping the book is a force known as
A) inertia.
B) friction.
C) the applied force.
D) the action-reaction force.

Answer 1

B. Friction. If the book was touching nothing, there would be no force to change its velocity given to it by the initial push. Because the book is sliding across the table, the molecules in the table are "slowing down" the book because they are exerting the force of friction on the book. What happens is that the charges in the book's molecules are attracted to the charges in the table's molecules. The attracting force is in the negative direction, causing the book to experience friction and therefore slow down.

Answer 2

A. inertia 

Because it has to do with the motion of something, especially if it changes its pace. In this example, the book's motion, when sliding on the table, decreased because of less force being given off from the student.