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Re: ROCKET ERROR



Hi Ludwik: You made two changes to your program. One was the fix I
suggested. But your second change was not only unnecessary but
actually incorrect, although it's only a smaller order error:

let dvR=-v0*dm/mR ! change of rocket m/s
let mR=mR-dm ! remaining rocket kg
let vR=vR+dvR ! new rocket speed

In this version of the program you calculate dvR from mR *before*
recalculating mR, whereas in your original program you calculated dvR
*after* recalculating mR. It was better the original way.

Roger dropped the second-order differential term dm*dvR. You should
not if you are going to let dm get rather large such as 10% of the
initial mass! By replacing the above three lines with:

let mR=mR-dm ! remaining rocket kg
let vR=vR-v0*dm/mR ! new rocket speed

you will not be dropping the second-order term and hence will improve
your program. (I leave the proof of this claim as an exercise.)
Cheers, Carl
--
Dr. Carl E. Mungan, Assistant Professor http://uwf.edu/cmungan/
Dept. of Physics, University of West Florida, Pensacola, FL 32514-5751
office: 850-474-2645 (secretary -2267, FAX -3323) email: cmungan@uwf.edu