Question

1. A textbook sitting on a table weighs 3.6 N. If you push straight down on the book with a force of 8.4 N, what is the normal force acting on the book?

Answer 1

The total force that is acting on the book downward is now the sum of the weight and pushing force:

$$F_d = 3.6N + 8.4N = 12N$$

Since the book does not move, the equal force should act on it upward. And this is the normal force from the table. Thus:

$$N = F_d = 12N$$

Answer. 12 N.