$"6-92.$ The second stage B of the two$-$stage rocket of mass $1\mathrm{.}2$ Mg $($empty$)$ is launched from the first stage with a relative velocity of $5400$km$/$h$.$ The fuel in the second stage has a mass of $350$ kg $.$ If it is consumed at the rate of $35$kg$/$s$,$ and ejected with a relative velocity of $2000$m$/$s$,$ determine the acceleration of the second stage B just after its engine is fired. What is the rocket's acceleration just before all the fuel is consumed? Neglect the effect of gravity and air resistance.

Prob. $6-92$