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1) Trains moving in opposite direction collide head on. 2) Moving train collides with stationary train 3) Trains moving in same direction collide head->rear. #1 has more energy that #2, #2 has more energy than #1. Because the relative speed between the trains is greater in #1 than #2 which is greater than #3.
@ankur, I wasn't sure if I should add this, but the stackexchange sites are also for reference for other people I the future (to prevent many nearly identical questions) so this 'answer' can help the OP and any visitor find the answer themselves.
@Gimamin, you put your hand (you know the thing you do things like eat with) on many door handles (or surfaces) that countless others with goodness knows what bacteria and germs have previously touched, so there are many things you touch that are equally unhygienic, especially as most people don't do it onto the seat but rather through the whole in the middle.
