Quote:

2) After the first acceleration the mass is moving and the pipe is moving in the opposite direction:
pMass = -1
pPipe = 1
pTotal = -1 + 1 = 0


Originally Posted By: paul
3) After the first turn the mass has the same speed but opposite direction.
pMass = 1
pPipe = 0
pTotal = 1 + 0 = 1

the mass presents its entire momentum to the pipe as it passes through the 1st turn.
this will cause the pipe to stop just as if the mass would stop the pipe if it were suddenly stopped by the pipe as it left the accelerator.


You say the mass's momentum changes by +2 units and the pipe's momentum changes by -1 units. Why the discrepancy?

Whatever momentum the mass transfers to the pipe, the pipe has to receive from the mass. If the mass gains 2, the pipe has to lose 2.


Another way to look at it:
Imagine the pipe and mass both have the same mass.
In step 2 it's effectively two identical objects travelling towards each other at the same speed.
You say that when they hit and bounce off, _one_ of them stops, while the other changes direction. How do you know which one stops and which one reverses?