Ok, so I'm answering without reading the other replies, cos I started to, and began to become influenced.
Large man- absolutely not, because I am then the cause of his death, without a doubt. If I don't act, I am an innocent bystander (who will forever have guilt and what ifs).
5 vs 1 - I am not sure. I think I would hope that someone in the group would see it and alert the others, whereas if I send it to the one guy, he might not see it. HOWEVER, maybe, on his own he is more alert and not distracted by conversation?! I don't know. My immediate reaction was 'of course I'd switch it', but I don't think I would, I think I would run and scream and see if I could get the tram conductors attention (hmmm, trams DO have conductors, right?).
Now I'm off to google this...