Question

1. Calculate the weight of a book with mass m = 800 g and the reaction force exerted by the table on the book. In which body is each of these forces applied?

Answer 1

By definition, the weigth of the block that does not move is:

$$P = mg$$

where $m = 800g = 0.8kg$ is the mass of the block, and $g = 9.8m/s^2$ is the gravitational acceleration. Thus:

$$P = 0.8\cdot 9.81 = 7.84N$$

This force is applied to the table. By the third Newton's law, the reaction force applied from the table to the block is:

$$N = P = 7.84N$$

Answer. Both forces are 7.84N. The weight $P$ is applied to the table, and the reaaction force $N$ is applied to the block.