I recognized that r=0.1 mm was too big (for covering the
tube length L at terminal velocity); that is why the largest
actually tabulated r was 0.01 mm.
I agree that a problem for which L=1 cm and rmin=9 cm.
for example, is more desirable than L=20 cm and rmin=5 cm.
Short L and large rmin allows to use the constant acceleration
(equal to rm*w^2, where rm is 9.5 cm. Right?) I think I know
how to compose the problem now. I will try to do this soon.
Ludwik Kowalski