Question

a 1000 kg rocket is fired from earth so that exhaust speed is 4200 m/s .then calculate rate of burning of fuel to provide initial thrust to over come its weight.

Answer 1

Thrust force on the rocket is counter balancing the weight of rocket

So we can use the formula of thrust force

$F_g = \frac{dm}{dt}* v$

$mg = \frac{dm}{dt}* v$

plug in all values in above equation

$1000* 9.8 = \frac{dm}{dt} * 4200$

$9800 = 4200*\frac{dm}{dt}$

now rate of gases exhaust is given by

$\frac{dm}{dt} = \frac{9800}{4200}$

$\frac{dm}{dt} = 2.33 kg/s$

so rate of mass is 2.33 kg/s