Rocket Propulsion - Varying mass

  • #1

Homework Statement


A rocket at rest in space, where there is virtually no gravitational force, has a mass of 2.55 * 105 kg, of which 1.81*105 kg is fuel.The engine consumes fuel at the rate of 480 kg/s and the xhaust speed is 3.27 m/s. The engine is fired for 250 s.
  1. Find the thrust of the rocket engine?


    [*]What is the mass of the rocket after the engine burn?
    [*]What is the final speed attained?

Homework Equations


Eq 1: Vf = Vi + Uexln |Mi/Mf|



The Attempt at a Solution


I think I know the first ine
Thrust = RUex
(480*3.27E3)

2 and 3 confuses me

Are they asking about Mass final? Shouldnt I find Vf first?
Mass Initial - 2.55E5
Mass Final after the fuel burns = 7.4E4

The answer for 2 is 1.35 E5 kg, 3 is 2.08E3 m/s

Thank you so much! :D
 

Answers and Replies

  • #3
you have got the rate of fuel consumption and removal. just use f = dp/dt (newton's original law)
 

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