Answer:

Step-by-step explanation:
Initially the rocket velocity is only on the x-axis. After the rocket suddenly shoots out one-third its mass parallel to the y axis, its velocity is in the x and y axes. Thus, According to momentum conservation principle, we have:
![mv_0=(2)/(3)mv_(x)\\v_x}=(3)/(2)v_0\\\\0=(1)/(3)m2v_0+(2)/(3)mv_(y)\\v_y=-(2)/(3)m(v_0)[(3)/(2m)]\\v_y=-v_0\\\\(0)_z=(0)_z\\v_z=0](https://img.qammunity.org/2020/formulas/physics/high-school/qubxmf5lox733m5b3lrw3e1hkg9qptavtt.png)
So, the velocity vector of the remaining rocket's mass is:
