A deep-space exploratory probe of total mass $3M$ is drifting through a region of negligible gravity at a constant speed $v$.

An internal spring-loaded mechanism is triggered, separating the probe into two components, X and Y, of masses $M$ and $2M$ respectively, as shown in the diagram.

Immediately after the separation, component X (mass $M$) continues moving in the original direction of travel but at an increased speed of $3v$. Component Y (mass $2M$) immediately comes to a complete rest.