Final answer:
The normal force on an object on an inclined plane exists as a reaction to the component of the object's weight acting perpendicular to the plane, as described by Newton's Third Law. For every action, there is an equal and opposite reaction, creating a balance between the downward gravitational component and the upward normal force.
Step-by-step explanation:
To explain the existence of the normal force acting on object P using Newton's Third Law, we begin by understanding that when an object is placed on a surface, the force of gravity pulls it down. According to Newton's Third Law, for every action, there is an equal and opposite reaction. Thus, the downward gravitational force that object P exerts on the inclined plane has a reactive force from the plane exerting upward on P, which is the normal force, N.
In the case of an inclined plane, the weight of the object is divided into two components: w₁, acting perpendicular to the inclined plane, and w₂, acting parallel to the plane. The perpendicular force component w₁ is countered by the normal force, which is equal in magnitude and opposite in direction (N = w₁). As a result of this action-reaction pair, the normal force exists, ensuring that object P does not accelerate through the plane.
If we take the incline angle to be θ and the mass of P to be 4 kg, the weight component perpendicular to the plane can be calculated as w₁ = m · g · cos(θ), where g is the acceleration due to gravity. This component will be balanced by the normal force, leading to N = w₁.