Questions & Answers about Я не знаю, почему куртка висит на крючке.
Why do we use висит на крючке here instead of вешает на крючок?
Висеть (here as висит) is an intransitive verb of state—it describes where something is currently located (the jacket is hanging). Because it describes a static location, it takes the Prepositional case (на крючке) to answer the question 'where?'. If someone were actively hanging the jacket up, we would use the transitive verb вешать with the Accusative case for destination: Он вешает куртку на крючок (He is hanging the jacket on the hook).
Is куртка the subject or object in the second half of the sentence?
It is the subject! Because висеть is a verb of state (meaning 'to be in a hanging position'), the jacket is the thing doing the action. That is why куртка is in the Nominative case. If it were the object being hung up by someone, it would be in the Accusative case (куртку).
The dictionary form for hook is крючок. Why is it spelled крючке here, without the 'о'?
The word крючок has a 'fleeting vowel.' In Russian, some masculine nouns lose the last vowel of their stem (usually о or е) when you add case endings. The base stem крючок drops the о to become крючк-, and then we add the Prepositional ending -е to get крючке.
Why is there a comma before ?