ANSWER
[tex]20m\/s[/tex]EXPLANATION
To find the velocity of the rocket, we have to apply the formula for momentum:
[tex]p=mv[/tex]where m = mass; v = velocity
Solve for the velocity:
[tex]\begin{gathered} 80=4\cdot v \\ \Rightarrow v=\frac{80}{4} \\ v=20m\/s \end{gathered}[/tex]That is the velocity of the rocket.
