First slide

Second law

Question

For a rocket propulsion velocity of exhaust gases relative to rocket is 2 km/s. If mass of rocket system is 1000 kg, then the rate of fuel consumption for a rocket to rise up with acceleration 4.9 m/s² will be :

Easy

A

12.25 kg/s
B

17 .5 kg/s
C

7 .35 kg/s
D

5.2 kg/s

Solution

$\begin{array}{l} Here, thrust = v \frac{dm}{dt} = (2000) \frac{dm}{dt} \\ For rocket, v \frac{dm}{dt} = m (g + a) \\ \Rightarrow 2000 \frac{dm}{dt} = 1000 (9 .8 + 4 .9) \\ \Rightarrow \frac{dm}{dt} = 7 .35 kg / s \end{array}$

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