Question
A $$600\,kg$$ rocket is set for a vertical firing. If the exhaust speed is $$1000\,m{s^{ - 1}},$$ the mass of the gas ejected per second to supply the thrust needed to overcome the weight of rocket is
A.
$$117.6\,kg\,{s^{ - 1}}$$
B.
$$58.6\,kg\,{s^{ - 1}}$$
C.
$$6\,kg\,{s^{ - 1}}$$
D.
$$76.4\,kg\,{s^{ - 1}}$$
Answer :
$$6\,kg\,{s^{ - 1}}$$
Solution :
$$\eqalign{
& {\text{Thrust}}\, = \frac{{udM}}{{dt}} = mg \cr
& \Rightarrow \frac{{dM}}{{dt}} = \frac{{mg}}{u} = \frac{{600 \times 10}}{{1000}} = 6\,kg\,{s^{ - 1}} \cr} $$