The first three are rather similar to each other as are the last three.
#1: A train is running on tracks that are about to fork. One path will run over a single individual who is tied down to the tracks, killing them. The other path will run over five individuals who are tied down to the track, killing them. You cannot stop the train. You must decide which path the train will take by flipping a switch. Which path are you obligated to choose (and are you obligated to act at all? Are you obligated to do nothing and to let the train run whichever way it was going to before your awareness of the dilemma?).
#2: A train is running on a single track that is destined to run over five individuals tied down to the track, killing them. There is a large individual whose mass you know will be enough to stop the train if he were placed in the train’s path. Pushing this individual into the path of the train (thus killing him) is the only way which the train can be stopped before it kills the five individuals tied to the tracks. Are you obligated to push the man into the path of the train? Are you obligated to do nothing? If your answer to this question is incongruous with your answer to #1 can you explain why?
#3: A laboratory has caught fire which contains many fertilized human embryos that are waiting to be implanted so that they may be born. Also in the building is a two-year old girl (presumably the daughter of someone who works there). You are in the unique position where you only have the time and the means to save either the two-year old girl or five of the fertilized embryos from dying in the fire. Obviously you are obligated to save one or the other. Which are you obligated to save? Why?
#4: An individual is about to murder someone right in front of you. You perceive this and realize the only way to stop the murder is to kill the perpetrator. Are you obligated to do this? Are you obligated to do nothing?
#5: Exact same scenario as #4 except in this case the perpetrator has legal authority to murder and you will face legal punishment if you kill him. The reasons this person has legal authority are bogus and his killing of the individual in front of you will still be the sin of murder. Are you obligated to kill the perpetrator under these circumstances? Are you obligated to do nothing? Does your answer to this question differ from your answer to #5? If so, why?
#6: A doctor is on his way to perform a legal abortion. You are the only person who can stop this from happening, but the only way to do it is by killing the doctor before he performs the abortion. Are you obligated to do this? Are you obligated to do nothing? How does your answer to this question compare to your answers to #4 and #5? If they differ substantially, why?