This is somewhat of a shower thought. Let's say there is a person with the same capabilities as superman. Would that person actually be able to stop an Asteroid from hitting earth? I can only image that a person with superhuman strength and speed would directly fly through the asteroid, not really stopping it but drilling a hole into it.
Edit: I guess too many think of this as a superhero question. Think of the person trying to stop the asteroid as a super hard, human shaped object hitting the asteroid at a high speed.