Because the mass you've moved forward also has to stop.

only in your mind , even if it you have been shown that it doesnt stop , it only needs to stop in your mind in order for your mind to accept it.

I suppose that when you were a child you didnt use the
little curvy sections of track and your train stopped when it ran out of track , you poor thing , somebody should have put the train track together for you.

Basic laws of physics, paul - every reaction has an opposite and equal reaction.

not really , not when its you that is describing action and reaction

according to you and kallog
a 50 kg force can stop a 450 kg force.

even if the two forces are constantly being applied towards each other.

450 kg ---->0 kg<----- 50 kg

they magically cancel each other out.

thats because you two guys are the smartest people on earth.

what I generally refer to as stupid smart people.

3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.