Question

A 600 kg rocket is set for vertical firing the exhaust speed is 800 m/s to given an initial upward acceleration of $20m/s^2,$ the amount of gas ejected per second to supply. The needed thrust will be :

• A. 137.5 kg/s
• B. 185.5 kg/s
• C. 187.5 kg/s
• D. 127. 5 kg/s

Answer 1

Answer: (C)

187.5 kg/s

Using the relation

$\left[\begin{array}{c}\frac{△m}{△t}\end{array}\right]v-mg=ma$

or $\frac{△m}{△t}\times \left(800\right)=m(g+a)$

or $800\times \frac{△m}{△t}=5000(10+20)$

or $\frac{△m}{△t}=\frac{5000\times 30}{800}$

or $\frac{△m}{△t}=\frac{1500}{8}=187.5kg/s$