Breakdown of Hän lukitsi näytön, koska hän tarvitsi uuden salasanan.
hän
he / she
uusi
new
koska
because
tarvita
to need
Questions & Answers about Hän lukitsi näytön, koska hän tarvitsi uuden salasanan.
How did we get lukitsi and tarvitsi from the dictionary verbs lukita and tarvita?
Both are Type 5 verbs. To form the past tense, you start with the present tense stem (lukitse- and tarvitse-) and change the final -e to the past tense marker -i. This gives us the past stems lukitsi- and tarvitsi-.
Why doesn't the hän form have a double vowel here, like it does in the present tense (hän lukitsee)?
In the past tense, the third-person singular form (hän) never doubles the final vowel. You simply use the past tense stem without adding any extra personal ending. That is why the verb stays exactly as hän lukitsi and hän tarvitsi.
Why do the words for screen (näyttö) and new password (uusi salasana) end in -n here?
They are the direct objects of the sentence. Because the actions are complete, these singular objects take the accusative case, which looks identical to the genitive -n ending. Notice that the adjective must match the noun, so both words get the ending: uuden salasanan.
Why does the word uusi (new) change so much to become uuden?