A question introduced by μη expects a negative answer. A question introduced by ου expects an affirmative answer. cf. BBG 31.20; Porter, Idioms, 277; Burton §467:
λέγει πρὸς αὐτὸν ὁ Νικόδημος· πῶς δύναται ἄνθρωπος γεννηθῆναι γέρων ὤν; μὴ δύναται εἰς τὴν κοιλίαν τῆς μητρὸς αὐτοῦ δεύτερον εἰσελθεῖν καὶ γεννηθῆναι;.
καὶ αὐτὸς ἦν ἐν τῇ πρύμνῃ ἐπὶ τὸ προσκεφάλαιον καθεύδων. καὶ ἐγείρουσιν αὐτὸν καὶ λέγουσιν αὐτῷ· διδάσκαλε, οὐ μέλει σοι ὅτι ἀπολλύμεθα;
The form οὐχί is a bit sharper in tone. (p1157)