Originally Posted by **ChipB** Couple of things you should clarify:
1. Please define the terms M_i and M_f.
2. This appears to be a problem involving a rocket acting in space, so that air resistance is ignored - hence the rocket's acceleration is solely a function of engine thrust and the rockets mass as a function of time. I think you shoudl state that assumption.
3. How did you derive the equation for final speed of the rocket? |

I actually clarified the terms M_i and M_f in the brackets, as being [(M_i -

**initial mass of the rocket + initial mass of the fuel**)/(M_f -

**final mass of the rocket**)].

Thanks about the hint in 2.

Concerning the point 3, the final equation was actually derived directly in the book, considering the systems of the rocket and the ejected fuel as an isolated system, which after equating the initial and final momentum of it and integrating gives as the

v_f-v_i = v_e*ln (M_i/M_f) , I got all the steps of this equation (even if not actively deriving it), but why are you asking me this? ... to make sure I use the right argument(equation) for my question?

Thanks