Impossible, I'm afraid Bruno. These are phrasal verbs and they are the torment of many learners of English. There is no easy answer - you just have to learn them all!
For these particular two phrasal verbs (you probably already know their meanings and usage)-
wake up - to stop being asleep. 'When the cat jumped onto the bed, I woke up suddenly.'
work out - to find the answer to a problem using your brain.
'Can you lend me a calculator? I can't work out this maths problem.'
'I bought this scanner two months ago, and I've only just worked out how to use it.'