Learn Swedish: Du borde sova, men du jobbar på med det mödosamma pusslet. - You ought to sleep, but you keep on working on the arduous puzzle.

The particle på after a verb adds a continuative aspect. It shows that an action is ongoing, persistent, or happening without interruption. While du jobbar simply means "you work," du jobbar på means "you keep on working" or "you work away."

The English translation says "working on the puzzle." Why does the Swedish use the preposition med instead of på?

In English, you work on a physical task or project, but in Swedish, you work with it (jobbar med). Additionally, since we are already using på as a continuative particle (jobbar på), trying to use it again as a preposition to mean "on" would sound incredibly awkward.

borde looks like a past tense verb, so why does the translation say "ought to sleep" instead of "ought to have slept"?

borde is historically the past tense form of the verb böra, but in modern Swedish, it functions as a present conditional meaning "should" or "ought to." If you actually wanted to express the past tense ("ought to have slept"), you would use borde ha sovit.

What is the exact nuance of mödosamma compared to a simpler word like svåra (difficult)?