Questions & Answers about Moje noge su umorne posle treninga.
Because moje has to agree with noge.
- noga = leg, feminine singular
- noge = legs, feminine plural
The possessive word moj changes form to match the noun:
- moja noga = my leg
- moje noge = my legs
So moja would be correct with singular noga, but not with plural noge.
Here noge is nominative plural because it is the subject of the sentence: the thing that is tired.
So in Moje noge su umorne, noge = my legs as the subject.
A useful detail: the form noge can mean different things in different contexts, including genitive singular, but in this sentence the verb su shows clearly that it is plural subject, so it must be nominative plural.
Su is the 3rd person plural present tense of biti = to be.
Since the subject is plural (noge), Serbian uses:
- je for singular