Problem 1.181

A spaceship of mass $m_{0}$ moves in the absence of external forces with a constant velocity $\mathbf{v}_{0}$. To change the motion direction, a jet engine is switched on. It starts ejecting a gas jet with velocity $u$ which is constant relative to the spaceship and directed at right angles to the spaceship motion. The engine is shut down when the mass of the spaceship decreases to $m$. Through what angle $\alpha$ did the motion direction of the spaceship deviate due to the jet engine operation?