Calculating Thrust from Rocket Engine Ejection Velocity

[recon223]

The burned gases of a rocket engine are ejected from the rocket nozzle at a speed of 17,000 ft/sec. If the weight of gas ejected is one pound per second, find the thrust developed by the rocket.


I don't really have an equation to use here but my guess is F = M\32.2 * Ejection Velocity


F in lbs. = [ 1 lb / 32.2] * 17,000 = 527 lbs of thrust


Anyone care to verify that this is correctly calculated or have any ideas on a different calcualtion?

 

[lewando]

Analysis of units does not support your approach. Also 32.2 ft/s² is the terrestrial acceleration due to gravity. The rocket could be anywhere-- interstellar space or the moon. Thrust is a function of the rocket, not gravity.

 

[RTW69]

Thrust=dm/dt*Vel

Your work looks correct to me. 1 lb_f=32.4 Lb_m*ft/Sec²
The units of thrust is lb_f

 

[lewando]

This part got me-- "the weight of gas ejected is one pound per second". I read this as a dm/dt of 1lb_f/s. If this is read as 1lb_m/s then things to fall into place.