Laws of Motion - Result Question 17
17. A $600 kg$ rocket is set for a vertical firing. If the exhaust speed is $1000 ms^{-1}$, 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) $76.4 kg s^{-1}$
[1990]
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Answer:
Correct Answer: 17. (c)
Solution:
- (c) Thrust = weight
$\Rightarrow \frac{u d M}{d t}=m g \Rightarrow \frac{d M}{d t}=\frac{m g}{u}$
$=\frac{600 \times 10}{1000}=6 kg s^{-1}$
