From: fortunati.luigi@gmail.com   
      
   I wasn't very happy with the way this discussion ended.   
      
   The case involved the elastic collision in the animation   
   https://youtu.be/wl0c6NMysY4 where the two bodies A and B collide at   
   equal and opposite velocities v and -v.   
      
   In the end, we concluded the discussion by discussing velocities v_A =   
   +1 m/s and v_B = -1000 m/s, which have nothing to do with what I had   
   asked, nor with the animation, where the two velocities are equal and   
   opposite.   
      
   I didn't have the presence of mind to clarify this, but now I'm ready to   
   do so by discussing the interesting clarifications that other comments   
   have highlighted.   
      
   We all agreed that (under the conditions of the animation) with the mass   
   of body A between "m" and less than "3m" both bodies recoil after the   
   collision, while with the mass of A greater than "3m," body A slows down   
   but continues to move forward without stopping.   
      
   What if the mass of body A is exactly equal to "3m"?   
      
   In this case, it doesn't go back or move forward.   
      
   So it stops.   
      
   But where does it stop?   
      
   I say it doesn't stop at the point x=0 where the collision occurs, but   
   at a point further forward in the previous direction of mass A.   
      
   This happens because, during the compression phase, the two bodies don't   
   remain stationary at the point x=0 but advance to the right, and only   
   then does body A stop, at the end of the elastic recoil.   
      
   It's as if body A of three train cars (moving to the right) and body B   
   of one train car (moving to the left) were to elastically collide on the   
   same track.   
      
   In this case, I expect the three train cars to stop at a point further   
   forward than the point (x=0) where the collision occurred.   
      
   Is this deduction correct?   
      
   Luigi Fortunati   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)