When stressed, the short vowels only occur in closed syllables.
Usually one occurs in a few specific places (closed syllables, say) and the other occurs everywhere else (open ones).
It works if one chooses the Latin, French, or Italian language, since German is much more difficult because of its many closed syllables and consonant clusters.
In final closed syllables, long u is usually shown by 'magic' e: amuse, flute, fume, huge, prelude, puce, puke, pure, refute, rude, rule, ruse, tube, tune.