# Homework Help: Homework help finding fraction of initial mass of rocket and fuel

1. Oct 14, 2009

### gadabout1018

1. The problem statement, all variables and given/known data

Obviously, we can make rockets to go very fast, but what is a reasonable top speed? Assume that a rocket is fired from rest at a space station in deep space, where gravity is negligible.

If the rocket ejects gas at a relative speed of 1100 and you want the rocket's speed eventually to be 1.00×10−3 c, where c is the speed of light, what fraction of the initial mass of the rocket and fuel is not fuel

2. Relevant equations

v=v(ex)ln(m/m0)
v1=1100lm(m/m0)

3. The attempt at a solution

i think im having trouble finding the final velocity. I did another poblem were the final velocity was 4000 m/s and i got it correct.

2. Oct 14, 2009

### JasonGodbout

The final velocity is 1.00×10−3 c.

3. Oct 14, 2009

### gadabout1018

that is what i thought but when i try in on mastering physics i get in incorrect

4. Oct 14, 2009

### JasonGodbout

Try e100 then e200 and you will see why.

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