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Hr.Tboy Group TitleBest ResponseYou've already chosen the best response.0
which one?
 one year ago

eseidl Group TitleBest ResponseYou've already chosen the best response.0
Answer is \[v_fv_i=u \ln (\frac{m_f}{m_i})\]I have no idea where the negative sign comes from. Here's what I did:\[m \frac{dv}{dt}=u \frac{dm}{dt}\]where u is a constant. so,\[dv=u \frac{dm}{m}\]and integrating:\[v_fv_i=u \ln (\frac{m_f}{m_i})\]I don't know where the negative sign come from....
 one year ago

AravindG Group TitleBest ResponseYou've already chosen the best response.1
you seechange in velocity dv is positive quantity whereas change in mass is negative
 one year ago

eseidl Group TitleBest ResponseYou've already chosen the best response.0
yeah the negative sign makes it work, and I agree it needs one. I just don't know how to justify it mathematically.
 one year ago

AravindG Group TitleBest ResponseYou've already chosen the best response.1
ots because u should have had ve sign in rhs from the first equation onwards!!
 one year ago

AravindG Group TitleBest ResponseYou've already chosen the best response.1
dw:1356100792938:dw
 one year ago

eseidl Group TitleBest ResponseYou've already chosen the best response.0
ok....it's confusing the way the instructor wrote it. If there were vector signs on v and u then it would make sense to add the negative sign once the vector arrows were dropped since v and u are in opposite directions. The instructor didn't do this though. Ok, thanks!
 one year ago
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