A marksman at rest fires a 4.00-kg gun that expels a bullet of mass 0.0140 kg with a velocity of 181 m/s. the marksman mass is 81.0 kg. what is the marksmans velocity after firing the gun?

Are we to assume that the marksman is standing on a frictionless surface (wearing ice skates perhaps)? If so, then conservation of momentum says that the momentum of the marksman + gun going backwards must equal the momentum of the bullet going forwards:


(m_{marksman}\ +\ m_{gun}) \times V = m_{bullet} \times V_{bullet}


Solve for V.