# Minimum thrust of engines at lift-off

by zebra1707
Tags: engines, liftoff, minimum, thrust
 P: 107 1. The problem statement, all variables and given/known data Hi there Rocket has a total mass of 3.4 x 10^6 kg at lift-off. The first stage contains 2.0 x 10^6 kg of propellants which is consumed at a rate of 1.4 x 10^4 kg s Find the minimum thrust of the engines at lift-off? I would have thought that you needed one more variable to be able to solve this? 2. Relevant equations 3. The attempt at a solution I used the mass flow x escape velocity and ended up with 15.7 x 10^6 N. It takes 142 sec for the first stage to finish its burn. I just dont think that this is right - as the next part states that if this thrust is sustained - find the time over which the first stage operates and the acceleration of the vehicle at that time. (Neglect air friction - and suume whole flight is vertical. Help needed please. Cheers
 P: 107 Any thoughts? Cheers
 P: 69 Wouldn't the minimum thrust just be m*g? In order to get the rocket moving, you would need at least 3.3*10^7 N of force.

 Related Discussions Mechanical Engineering 20 General Engineering 75 Advanced Physics Homework 2 Beyond the Standard Model 3 Mechanical Engineering 5