Rocket Propulsion - Varying mass

[P-Illiterate]

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: V_f = V_i + U_exln |M_i/M_f|

The Attempt at a Solution

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

2 and 3 confuses me

Are they asking about Mass final? Shouldnt I find V_f 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

 

[P-Illiterate]

I got the answer!

 

[ashishsinghal]

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