Derive the law of conservation of momentum from Newtons thirds law?

Deduce law of conservation of momentum from Newton's third law of motion. Consider two bodies A and B of masses mA and mB moving in the same direction along a straight line. ... Thus, total momentum of the two bodies is conserved provided no external force acts on them. This proves the law of conservation of momentum.

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the box does not move because you need to use a force greater than 300 n. you are only using 50 n. it needs to at least be 301 n for the box to move because then it is an unbalanced force and it will move the way that the greater force is pushing it. if you use only 300 n it will be a balanced force and will not move because the force you are exerting on the   box is the same as its force.

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im sorry if i went too in depth, i am going to include a link to a video on khan academy that will explain this.   hope that you like the video and that it explains more in detail to you.

that is the link.

elctricity and magnet is conversion to it