Hit the 5.
Well consider, why would they be on the tracks? Tying 5 people up is kind of odd to begin with... one can figure the chances are they probably had such done to them as a punishment, as no villian ties up *FIVE* people. One usually, two tops.
The one on the other tracks is likely a diversion for people who are 'trying' to be just... the idea of having 5 murderers on one side, and an angel on the other, how better to screw with someone's mind than trick them into killing an angel of their own free will?
If they REALLY wanted that ONE person to die, they'd just put them on the same tracks as the other 5. The fact that there's not 3 and 3, implies they're not equally deserving of death by the mind of whoever put them there. The further fact that one is equal to five, implies that they are trying to guide yeur hand into hitting the one, and I don't like being manipulated like that.
As for emergency brakes? I think yeu underestimate how much stopping power a train needs. Generally it takes a train/trolley literally kilometers (or several miles) to come to a stop. By the time they see someone on the tracks, it's already too late. It takes minutes of braking to actually come to a complete stop.
The second question's just stupid though. If that person's 'wide' enough to stop the sheer power of a TRAIN, then there's quite literally no way I can move them at all, let alone push them off a bridge. In terms of morality, the question would be, why is that one person not tied up? They could be the warden or executioner, and the other 5 could deserve it.
Think the quote "there's many who live who deserve to die, and many who die who deserve life, can yeu give it to them?" kinda applies here... there's no way to know all ends. Value of life by raw numbers isn't that easy to do. Do yeu sacrifice a million to save a thousand? Or vice versa?
The examples here are some of the worst I've seen though, so I really don't think it's that good of a question on either case.