Quote:

1. accelerate 20 masses applies 20 positive forces.

OK, impulse = +20
The pipe's moving forward with momentum +20

Quote:

2. turn 1 mass around 180 degrees applies a negative force.

-2 because it's reversing not just stopping.

Now we have to consider the actual possible layout. I suppose those 20 masses were spaced apart in their accelerator to begin with - or all lumped together. Either way, before any masses get to the 2nd u-bend, which I suppose is at the opposite end of the tube, all the other 19 have reached their first turn-around -

-2 * 19 = -38
Total = +20 - 2 - 2*19 = -20
Now the pipe's going backwards with momentum -20

Quote:

3. turn 1 mass around 180 degrees applies a positive force.

+2

Then the other 19 masses do their 2nd turn-around -

+2 * 19 = +38

Total = +20
Now the pipe's moving forward again with momentum +20


What next?





Edited by kallog (06/19/10 03:02 PM)