Determine the power of the jet engine of an airplane

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SUMMARY

The discussion focuses on calculating the power output of a jet engine based on specific parameters: an intake of 130 kg of air per second and a fuel consumption of 4.3 kg per second, with exhaust gases exiting at 600 m/s while the airplane travels at 260 m/s. The initial approach using the formula W = v^2(DM/DT) was identified as incorrect due to the misunderstanding of momentum change. The correct method involves applying Newton's second law, emphasizing the need to account for the rate of change of momentum to determine the force exerted by the engine.

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  • Understanding of Newton's second law of motion
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Fisicks
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Homework Statement


The jet engine of an airplane takes in 130 kg of air per second, which is burned with 4.3 kg of fuel per second. The burned gases leave the plane at a speed of 600 m/s (relative to the plane). If the plane is traveling 260 m/s, determine the power (hp) delivered.


Homework Equations


P=Fv
M(DV/DT)=F_ext + v_rel(DM/DT)



The Attempt at a Solution


dv/dt=0 so F=v_rel(DM/DT)
Thus W=v^2(DM/DT)=(600^2)(4.3) but this is incorrect and I do see where I am wrong.
 
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Hi Fisicks! :smile:

You've used mdv/dt, which obviously doesn't work if m is not constant :redface:

(and dv/dt = 0, which I don't really understand)

start again, using the full version of good ol' Newton's second law …

force = rate of change of momentum :wink:
 

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