Question

Prove that the momentum remains conserved using newton's third law

Answer 1

When two objects collide, in the absence of any additional external forces acting on the pair of objects, momentum is conserved precisely because the collision is just an interaction between the two objects. That is, it’s a Newton’s third law problem. That interaction between the objects exerts equal and opposite forces on each one. And those forces act for exactly the same amount of time - the time the objects are in contact, so they exert equal and opposite impulses on each other. That is a result of Newton’s third law.