# A multi-stage rocket

1. Feb 26, 2008

### faller217

I was hoping someone could help me with this homework problem that has me stumped. Any assistance would be appreciated.

Suppose the first stage of a two-stage rocket has total mass 1.30×10^4 kg, of which 1.10×10^4 kg is fuel. The total mass of the second stage is 1000 kg, of which 700 kg is fuel. Assume that the relative speed v_ex of ejected material is constant, and ignore any effect of gravity. (The effect of gravity is small during the firing period if the rate of fuel consumption is large.)

A) Suppose the entire fuel supply carried by the two-stage rocket is utilized in a single-stage rocket with the same total mass of 1.40×10^4 kg. In terms of v_ex, what is the speed of the rocket, starting from rest, when its fuel is exhausted?

B)For the two-stage rocket, what is the speed when the fuel of the first stage is exhausted if the first stage carries the second stage with it to this point? This speed then becomes the initial speed of the second stage. At this point, the second stage separates from the first stage.

C)What is the final speed of the second stage?

D)What value of v_ex is required to give the second stage of the rocket a speed of 6.00 km/s?

2. Feb 26, 2008

### D H

Staff Emeritus
We don't do your homework for you. Please show some work. What are the relevant equations for this kind of problem?