Recent content by Corsair

Ok I get it. I made two mistakes: I forgot the momentum I used was an expansion; and dv in rocket rest frame is different from dv on earth. So let me call the velocity in rocket rest frame u. Initially the 4-momentum is (mc, 0). After dt time, the 4-momentum of the rocket is ((m - dm)c...

This is what I am thinking now. I still need two equations: one for momentum, the other for mass-energy, right?

Sorry, that was a typo.. When I was trying to solve it, my goal WAS the correct equation.:blushing: Thanks for your reply!

That should work. But --- maybe my understanding is wrong --- shouldn't these two methods be equivalent?

Sorry guys. That was not a square root... My bad. I don't have that book right now, sorry. I haven't read Count's solution yet. :-p I'll try jdwood983's method first.

This is actually a problem in Goldstein. Homework Statement A rocket that ejects stuff at a speed a in its rest frame. Demonstrate that m\frac{d v}{dm} + a\left(1 - {v^2 \over c^2}\right) = 0 in which m is the invariant mass of the rocket and v is the velocity of the rocket viewed in Earth...