Irritating question/lost thread

Hey

I'm sure I read this here on an ATS thread but can't find the link in a search.
******************
Insect, flying East, hits express train going West. Insect is suddenly transformed from going at say 20 mph EAST to 120 mph WEST. For an instant, the insect is going to be at zero mph.

So does this mean the express train is at zero mph for an instant too?
******************

Can some kind soul link to the thread, or better still answer me because IT IS SENDING ME INSANE.



TD