Questions & Answers about Moje kolano jest zimne.
Why is it Moje instead of Mój or Moja?
Kolano (knee) is a neuter noun because it ends in -o. In Polish, words like 'my' have to match the gender of the noun they belong to. So, we use the neuter form moje instead of the masculine mój or the feminine moja.
Why do we use the adjective zimne here instead of zimno?
Here, you are describing a physical object (the knee), so you use the neuter adjective zimne. You only use the word zimno when talking about how a person feels overall (like Jest mi zimno - I am cold) or the weather (Jest zimno - It is cold outside).
Since 'I am cold' is Jest mi zimno, can I say Jest mi zimne kolano?
No, you cannot mix those two sentence structures. If you feel cold overall, you use Jest mi zimno (literally: it is cold to me). But when a specific body part is physically cold to the touch, you just describe it like a normal object using the subject and an adjective, exactly like in English: Moje kolano jest zimne.
If I wanted to say 'His knee is cold', would the adjective zimne change?