Question

A pool table has a mass of 600 kg. In an attempt to move it, Peter exerts an upwards force of 1000 N on the pool table. What is the normal force now acting on the pool table?

Answer 1

The total weight of the table (the force the table exerts on the floor) is:

$$W = mg - 1000N$$

where $m = 600kg$ is the mass of the table, $g\approx 10N/kg$ is the gravitational acceleration, and $1000N$ is the Peter's force. The minus sign is due to the fact, that the gravity force $mg$ is directed downward, and Peter's force is directed upward.

By the third Newton's law, the normal force acting on the pool table is equal to its weight:

$$N = W = 600\cdot 10 - 1000 = 5000N$$

Answer. 5000N.