Question

Conservation of linear momentum is equivalent to:
A) Newton’s first law of motion
B) Newton’s second law of motion
C) Newton’s third law of motion
D) Newton’s law of gravitation

Answer 1

Hint: Law of conservation of linear momentum states that the total linear momentum of a system always remains constant, i.e. before and after a collision occurs. Compare this law with the others given in the options. Whichever law, given in the options, best matches in meaning with this law, will be the answer to the question.

Complete answer:
According to the law of conservation of linear momentum, the total linear momentum of a system of several bodies remains constant before and after any collision occurs. i.e. the linear momentum is conserved. Now, we will look at the options one by one and check which option best matches, in meaning, with the above law.
Option A: Newton’s First law of motion
This law states that any object which is at rest or, in motion, will continue to be in its state of rest, or motion, respectively until an external force is made to act upon it.
This doesn’t convey the same message as that conveyed by law of conservation of mass. This is not the correct option.
Option B: Newton’s Second law of motion
This law states that the acceleration of an object currently in motion is directly related to the net force acting on it and inversely related to the mass of that particular body.
This doesn’t convey the same message as that conveyed by law of conservation of mass. This is not the correct option.
Option C: Newton’s Third law of motion
This law states that every action, in the physical world, will surely have an equal and opposite reaction.
If we look closely, this law is in accordance with the law of conservation of linear momentum as when two bodies collide, they both exert an equal amount of force on each other that they experienced through the other body and hence, the entire momentum of the system is conserved.
Hence, Option C is the correct answer.
Option D: Newton’s law of gravitation
This law states that the gravitational force between two objects is directly proportional to the masses of each of the bodies and inversely proportional to the square of distance between them.
This doesn’t convey the same message as that conveyed by law of conservation of mass. This is not the correct option.

Note: Whatever we experience in our everyday life is in accordance with Newton's third law of motion. Whether it be writing on a paper, being able to walk, or getting hurt after punching a wall, all these are explained by Newton's third law of motion. This is why this law holds such importance in mechanical physics.