Question

A 30kg crate rests on a horizontal floor, and a 70kg person is standing on the crate. Determine the magnitude of the normal force that the floor exerts on the crate.

Answer 1

N=100Kg

Step-by-step explanation:

On the vertical, the forces acting on the person are its weight (downwards) and the normal from the crate to the person (upwards). They are equal since the person is standing still. That normal force has a reaction on the crate, which is the normal from the person to the crate (downwards), of equal magnitude than the normal from the crate to the person. This force adds up with the weight of the crate (downwards), and both must equal the normal from the person to the crate (upwards). Its magnitude will be then the sum of the weights of the crate and the person, N=100Kg.