Question

A 5000 kg rocket is set for vertical firing. The exhaust speed is 800 `m//s`. To give an initial upward acceleration of 20 `m//s^(2)`, the amount of gas ejected per second to supply the needed thrust will be (Take `g = 10 m//s^(2)`)
A. `127.5 kgs^(-1)`
B. `187.5 kgs^(-1)`
C. `185.5 kgs^(-1)`
D. `137.5 kgs^(-1)`

Answer 1

Correct Answer - B
(b) `F=u(dm)/(dt)=m(g+a)`
`implies" " (dm)/(dt)=(m(g+a))/(u)=(5000xx(10+20))/(800)=187.5 kgs^(-1)`