The equation of motion for rockets is where is the speed of the exhaust shooting out the back. The final velocity of the rocket is a few multiples of the exhaust speed, so it's quite important, but in physics textbooks, is usually treated like a freely adjustable parameter whose origin and precise value is a detail left for engineers to worry about. With a little bit of approximation, we can do better than that.
Estimate for the combustion of methane the propellant used by SpaceX for its Raptor rocket engine program.
Details and Assumptions: