How does newton's first law affect human motion?

Consider a system to be two train cars traveling toward each other. what is the total momentum of the system before the train cars collide?   kg • what must the total momentum of the system be after the train cars collide?   kg •  

An object resting on a table weighs 100 n. with what force is the object pushing on the table? with what force is the table pushing on the object? explain how you got your answer.

Aforce or 500 n separates two objects the distance between their centers is 67 m the first object has a mass of 20kg what is the mass of the second