Life In 19x19

EDIT:
moved to physics thread

The relative speed of insect and train was 0 for a moment (and since the body of the insect is likeley to stay on the train probably for longer).
The speed of the train relative to earth was never 0 during the incident.
The speed of the insect relative to earth might have been 0 during the incident. If the insect was moving in the same direction as the train before the impact the speed doesn't go to 0, if it was moving in the opposite direction of the train it goes to 0 very shortly. But since the insect gets deformed during that process defining its speed is a bit hard.

I have no clue what you want to say in your last paragraph.

m(Train)*v(Train)+m(Train)+v(insect) is constant at all times (disregarding friction)