После работы я устал, но доволен днём.

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Breakdown of После работы я устал, но доволен днём.

• день: the day
• работа: the work
• но: but

Questions & Answers about После работы я устал, но доволен днём.

Why is работы used after после, and what case is it?

После always takes the genitive case.

• The noun работа (work) in the genitive singular is работы.
• So после работы literally means after (the) work.

Pattern to remember:

• после чего? – after what? → genitive
  
  • после урока
  • после встречи
  • после войны

What is устал grammatically, and why isn't there a separate word for was?

Устал is:

• the past tense, masculine singular form of the verb устать (to get tired),
• which is a perfective verb (focus on result: became tired / ended up tired).

In Russian past tense, you usually don’t use a separate word for “was” with such forms:

• я устал = I got tired / I am tired (as a result)
• Literally: I-tired (masc., past)

The idea of “was” is built into the past form устал, so you don't say something like я был устал in normal speech.

How would устал change for a woman or for more than one person?