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# A rocket burns fuel at the rate of $200 kg/s$. The exhaust gases are ejected down with a velocity of $400 m/s$. The upthrust developed by the rocket engine is

$(a)\;8 \times 10^5 N \quad (b)\;4 \times 10^5 N \quad (c)\;4 \times 10^4 N \quad(d)\;8 \times 10^4 N$

$F=v \large\frac{dm}{dt}$
$F=400 \times 200$
$\quad=8 \times 10 ^4 \;N$
Hence d is the correct answer.

edited Jan 26, 2014 by meena.p