Laws Of Motion Question 205
Question: A 5000 kg rocket is set for vertical firing. The exhaust speed is $ 800m{{s}^{-1}} $ . To give an initial upward acceleration of $ 20m{{s}^{-2}} $ , the amount of gas ejected per second to supply the needed thrust will be $ (g=10m{{s}^{-2}}) $ [CBSE PMT 1998]
Options:
A)$ 127.5kg{{s}^{-1}} $
B) $ 187.5kg{{s}^{-1}} $
C) $ 185.5kg{{s}^{-1}} $
D) $ 137.5kg{{s}^{-1}} $
Show Answer
Answer:
Correct Answer: B
Solution:
$ F=\frac{udm}{dt}=m(g+a) $ therefore $ \frac{dm}{dt}=\frac{m(g+a)}{u} $
$ =\frac{5000\times (10+20)}{800} $
$ =187.5\ kg/s $
