Fuel velocity vs exhaust velocity difference?

[liddojoe]

hi all,

i've been confused about what the difference is between fuel velocity and exhaust velocity. apparently, fuel velocity is equal to rocket velocity minus exhaust velocity. attached are screenshots of the textbook reading that confused me. if anyone can explain this section to me, i would greatly appreciate it!

thanks!
joe

 

[tiny-tim]

hi joe! welcome to pf!

i've been confused about what the difference is between fuel velocity and exhaust velocity. apparently, fuel velocity is equal to rocket velocity minus exhaust velocity.

fuel velocity, v_fuel, is the velocity of the fuel (relative to earth)

exhaust velocity, v_ex, is the velocity of the fuel relative to the rocket

v_ex is constant (because the rocket engine has constant power)