91Ó°ÊÓ

Normal force is a supportive force that acts perpendicular to surfaces of contact. It is what prevents objects from just falling through a surface. When you stand on a floor, there is an upward normal force, essentially the floor pushing back up against your weight.
In the exercise, the normal force exerted by the floor on the passenger is 620 N upwards. This force is vital because it counteracts the force of gravity pulling the passenger downwards.
One crucial aspect of the normal force is that it changes depending on the situation. If an elevator accelerates upwards, for instance, the normal force will increase to counteract this additional force. Conversely, if the elevator moves down, the normal force decreases.
It’s important to remember that according to Newton's third law, there is a reaction force acting down with the same magnitude when a normal force is present.

Gravitational force is the force with which the Earth pulls objects towards its center. This force is responsible for giving objects weight. The gravitational force (or weight) of an object can be calculated using the formula: \[ F_g = mg \] where - \( m \) is mass, and - \( g \) is the acceleration due to gravity (approximately 9.8 m/s² on Earth).
In the given problem, the gravitational force acting on the passenger is 650 N downward. This indicates the Earth's pull on the passenger. Unlike the normal force, the gravitational force remains fairly constant for an object near the Earth's surface.
For every gravitational pull the Earth exerts on an object, there is an equal and opposite force that the object exerts back on the Earth, maintaining the balance described by Newton's third law.

The net force is the total force acting on an object when all individual forces are combined. It determines the object’s motion according to Newton's first and second laws. - When an object has multiple forces, like in the exercise, the net force is calculated by vectorially adding those forces together.
For this particular exercise, \[ F_{net} = F_{normal} - F_{gravitational} = 620 \, \mathrm{N} - 650 \, \mathrm{N} = -30 \, \mathrm{N} \]
This results in a net force of -30 N, indicating a net downward force acting on the passenger. The negative sign shows that the direction of the net force is the same as that of gravitational force, making the passenger feel lighter. When the net force is not zero, the object will accelerate in the direction of the net force, according to Newton's second law.

Acceleration is a change in velocity that happens when objects experience net force. This can be computed using Newton's second law, represented by the equation: \[ F = ma \] where - \( F \) is the net force, - \( m \) is the mass, and - \( a \) is acceleration.
In the problem, after finding the net force to be -30 N, the mass of the passenger is calculated using their weight (gravitational force): \[ m = \frac{650 \, \mathrm{N}}{9.8 \, \mathrm{m/s^2}} \approx 66.33 \, \mathrm{kg} \]
Then the acceleration is calculated as: \[ a = \frac{-30 \, \mathrm{N}}{66.33 \, \mathrm{kg}} \approx -0.45 \, \mathrm{m/s^2} \]
This acceleration value indicates that the passenger is accelerating downwards at 0.45 m/s². The direction and magnitude of acceleration depend directly on the net force and mass.