The rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of the force. This rule is known as:

Correct option is A

​The correct answer is (a) Newton's Second Law of Motion.

Newton's Second Law of Motion states that the rate of change of momentum of an object is directly proportional to the force applied to it and occurs in the direction of the force. Mathematically, this law is expressed as:

where:

$$F= \frac{d}{dt} (mv)$$​​

• F is the applied force,
• m is the mass of the object,
• v is the velocity of the object, and
• $$\frac{d}{dt} (mv)$$​is the rate of change of momentum.

Information about the Other Options:

• Newton's Fourth Law of Motion: There is no "Fourth Law" in Newton's laws of motion. Newton formulated three fundamental laws of motion.
• Newton's First Law of Motion: Newton's First Law(also known as the Law of Inertia) states that an object will remain at rest or in uniform motion unless acted upon by an external force. 
• Newton's Third Law of Motion: Newton's Third Law states that for every action, there is an equal and opposite reaction. 

Information Booster:

• The second law of motion explains how the velocity of an object changes when a force is applied to it. The force is proportional to both the mass and the acceleration of the object.
• This law forms the foundation of classical mechanics, helping us understand the relationship between force, mass, and acceleration.