The specific meaning is the same. There are slightly different implications though. The first version sounds more demanding - so would typically be said by a parent, or a boss. People would typically add something like 'yet' at the end to make it a bit more polite, or 'have you managed to finish it'. The second, as Michelle sort-of said, suggests that there was an implied deadline for the task. There is an implication (from the 'some time in the past' timing of the tense) that it should have been finished before the question is asked.

I'm not too sure on the difference in meaning, but I am way more likely to say "did you finish it" if I'm speaking to someone. The first isn't wrong but feels a bit stilted.

They both express the same idea, if the task was completed or not. As the grammar rules define each one, Past simple and presente perfect, the difference between both sentences is the time they refer to. Have you finished it (now)? Have you finished it (yet)? Was the task completed by the moment of speaking? Did you finish it (then)? Was the task completed by the time given? I hope it helps :)