Yesterday I asked a question about the meaning of "научись," and it turned out that in the movie in which I heard this, it was not "научись," but "на, учись." This was a real trap! The Russian phonetics is so tricky!
Kind users of this forum explained to me that the particle на in "на, учись" is somewhat more stressed than the prefix на in "научись" is, and I got curious whether this is a general principle to distinguish between prefixes and separate words and whether I should always stress words that could be taken for a prefix.
My question is this: What is the difference in pronunciation between:
(1) "Зачем пришел?" ("Why did you come?") and "за чем пришел?" ("What thing did you come to take?").
(2) "Выхóдите гулять?" ("Are you going out to walk now?") and "Вы ходите гулять?" ("Do you regularly go to walk?").
(3) "Он невежливый" ("He is impolite") and ""он не вежливый" ("He is not polite").
(4) "Давайте порублю" ("Let me cut") and "давайте по рублю" ("Give me one rouble each").