Question

A book exerts a force of 2N downwards into a chair. The chair exerts a force of 5N downwards to the floor it stands on.
What is the force that the floor exerts upwards on the chair?

Answer 1

Answer:

7N

Explanation:

By Newton's third law, for every reaction there is an equal and opposite reaction. The floor must exert a 7N force upwards on the chair for the system to remain at rest. If it exerted less than that, the chair would be accelerating into the floor. This force, exerted by a surface, perpendicular to it, is called the normal force.

Answer 2

Answer: 5N .

Explanation: The 3rd law of motion by Newton states that in every action, there is an opposite and equal reaction. It is the Law of Interaction. The forces of each objects don't cancel each other.

When an object exerts force to another object, the other object also exerts equal force into it. But they are opposite in directions.