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## Homework Statement

A rocket at rest in space, where there is virtually no gravitational force, has a mass of 2.55 * 10

^{5}kg, of which 1.81*10

^{5}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.

- 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

_{ex}ln |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