A rocket, mass m=4000kg, lifts off the ground vertically with acceleration of a=0.2g. The velocity of gass emmiting from it is u=1200m/s (with respect to the rocket). Find engine's reactive force and then fuel burn rate (mu).(adsbygoogle = window.adsbygoogle || []).push({});

This is what i managed to do:

rocket's speed at any moment t (with respect to the ground) isa*t

gass's speed at any moment t (with respect to the ground) isu-a*t

Mass of rocket at any time t ism-mu*t

Mass of fuel that is burned ismu*t

rocket's mass multiplied by it's speed and gass's mass multiplied by its speed are equal, so

(m-mu*t)*a*t=mu*t*(u-a*t)

and i get thatm*a*t=mu*t*u

mu=(m*a)/u=6.53 kg/s

but... I was given 4 answers (5.9kg/s 9.8kg/s 39.2kg/s 19.8kg/s) and mine is wrong...

Any ideas anyone?

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# Homework Help: Fuel burn rate

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