How Is Velocity Calculated for a Two-Stage Rocket?

[engineertech0]

Homework Statement

In a two-stage rocket, the exhaust velocity for the first stage burn is 3000 m/s and for the second stage burn is 3000 m/s. Assume that during the entire sequence of burns the rocket is still near enough to the surface of the Earth to approximate the external gravitational acceleration as 9.8m/s^2 , and ignore air resistance. The mass of the first stage engine and tanks is 2000kg. The mass of the fuel held in the first stage is 4000kg. The first stage fuel burns in 10 seconds. The first stage is then ejected. The mass of the second stage engine, tanks, and payload is 2000kg. The mass of the fuel held in the second stage is 2000kg. The second stage fuel burns in 5 seconds. (The second stage tanks remain attached to the payload when empty.) (a) At what speed is the second stage/payload combination moving at the end of the second stage burn? (b) How much faster is this than the speed if all the 6000kg fuel were burned in the first stage in 15 seconds with the same exhaust velocity (3000m/s) and the entire 4000kg assembly of the empty rocket remained in one piece?

Homework Equations

(d=v*t) (v=d/t)

The Attempt at a Solution

 

[Filip Larsen]

What have you tried so far and where are you stuck?

Do you know how to calculate speed change for a single-stage rocket (hint: rocket equation)?