Jet engine thrust and power with air intake and fuel burn

[mwingboy]

Homework Statement

A jet aircraft is traveling at 246 m/s in horizontal flight. The engine takes in air at a rate of 77.0 kg/s and burns fuel at a rate of 4.00 kg/s. If the exhaust gases are ejected at 633 m/s relative to the aircraft, find the thrust of the jet engine and the delivered power.

find thrust and power

ive tried everything! even my teacher couldn't get the problem. but i refuse to just accept that i can't get it..please help would be greatly appreciated!

 

[nasu]

If you've tried everything maybe you could show at least some of it.

 

[mwingboy]

ahh yes, sorry about that.

here's what i know. i know that it change in momentum is obviously is impulse. So i have it set to a 1 second time frame, and i found:

initial momentum = ((77 kg + 4 kg) * 246 m/s) = 19926 kg*m/s
TOTAL MASS * VELOCITY = Momentum

final momentum = ((77 kg + 4 kg) * -387 m/s) = -31347 kg*m/s
TOTAL MASS * VELOCITY = Momentum

the change in that would become the average force because impulse (which is change in momentum) is equal to average force * time. and the time is set to 1 in this instance.

anybody see flaws in the thinking?