Learn Polish: Jesteś zmęczony przed podróżą? - Are you tired before the trip?

The preposition przed (before) requires the following noun to be in the Instrumental case when it is used to talk about time. Because podróż (trip) is a feminine noun, it takes the standard feminine Instrumental ending -ą.

Wait, is podróż a feminine noun? It doesn't end in an '-a'.

Yes! While most Polish feminine nouns end in -a, there is a special group of feminine nouns that end in a consonant, such as podróż (trip), noc (night), and rzecz (thing). Even though its base form ends in a consonant, it still behaves like a feminine noun and gets the -ą ending in the Instrumental case.

If I am asking a female friend this question, does the sentence change?

Yes. The adjective zmęczony (tired) is in the masculine form here, which means the speaker is talking to a man. To ask a woman, you must change the adjective to its feminine form: Jesteś zmęczona przed podróżą?

Why isn't the word ty (you) used in this sentence?

In Polish, subject pronouns are usually dropped because the verb form already tells you who is doing the action. Jesteś clearly means 'you are', so Polish speakers only add ty if they want to emphasize 'you' specifically, like when contrasting you with someone else.