1) I would pull it. However I would first try to untie that one person. This act is indirect.

2) I would not push the 'fat man' as there is no guarantee he would stop the train....what is his weight? 1000pounds or something o.o....Even if I tried to push him, he would easily overpower me and I may instead be the one being thrown infront the train...

Also this act is direct, no way am I gonna willingly kill a man in such a situation. If I did, I would clearly be a cold and heartless bastard, with no regard for human life or anyone standing next to me.

3) Basically the same ans. as no. 2


Edit: I just realized that there is no true measure to the value of life, however life is to be highly valued. The one person separate person tied to the track would represent me. In this case I would have given my life to save the other five people.

In the case of the 'fat man', this fat man would also represent 'me', of course in this case I would not have liked to have been shoved unto the train tracks by some random person and of course I would have given up a fight.