He is in a treehouse or an attic and there is a hatch in the floor.

He was a fisherman. He phoned home to tell his wife that he had caught a very big fish and like all fisherman do, he stretched both his arms to indicate how big the fish was, accidentally put his hands through the glass of the phonebooth, cut both his  wrists and bled to death. He should have brought his mobile phone.

He puts something into the barrel with a lower density than oil. The oil will spill out of the barrel and the whole contraption weighs less than before. A big block of wood would do the trick.

It was a men only hotel and the stranger was a woman, who knocked on the door to check if anyone was in the room. (and if there wasnot she would have burglarized the room).

The doctor had taken out his own wife’s appendix 3 years ago. Donald is also a doctor. The doctor Donald called is surprised that Donald will not take out the appendix of his (Donald’s) wife himself.