conservation of momentum is the philosophic or
OK so we don't use momentum at all anymore in this discussion.
I repeat a 4000N force can accelerate a 1000 kg mass
to 4 m/s/s in 1 second , that mass will move a distance of
2 meters.
I agree.
also , there is no additional force applied to the pipe
in the direction that would reverse the pipes direction.
During that acceleration? Yes I agree to that too.
you do agree that the 100kg mass traveling at 40 m/s
passing through the 1st turn will apply a 4000N force
to the 1st turn , correct?
It should be a negative force applied to the turn. And its magnitude is free to be whatever you choose, so yes I agree it can be -4000N.
and that this 4000N force will apply to the pipe, correct?
Yes but in the negative direction.
so if you agree on the above then the pipe will slow
from 4 m/s velocity to 0 m/s velocity in 1 second , correct?
Yes I agree on that too.
Do agree that the same 1st turn will also apply a 4000N force to the mass, in the opposite direction to its motion?
If you agree on that, then you should also agree that the mass will slow from -40m/s velocity to 0m/s velocity in 1 second, correct? Here's how:
F=ma
4000N = 100kg * 40m/s^2
So it slows from -40m/s to 0 in 1 second.
Now the pipe's stopped, and the mass has stopped too. So the turnaround isn't complete. The mass needs to get back up to 40m/s in the opposite direction. Doing that will start moving the stationary pipe too.
