Breakdown of Neću kupiti novu tipkovnicu kojom je teško raditi.
biti
to be (sam, si, je)
nov
new
težak
difficult / severe, serious
raditi
to work
Questions & Answers about Neću kupiti novu tipkovnicu kojom je teško raditi.
Why is the relative pronoun kojom in the instrumental case, and why isn't there a preposition like s (with) before it?
The relative clause literally translates to "with which it is hard to work". In Croatian, when you use an object as a tool or instrument to perform an action (like using a keyboard to type), you use the instrumental case without the preposition s. You generally only use s for company, such as working alongside a person.
tipkovnicu is in the accusative case. Why isn't the relative pronoun in the accusative case too?
A relative pronoun always copies the gender and number of the noun it refers to. Since tipkovnica is feminine singular, the pronoun is too. However, a relative pronoun's case depends entirely on its job inside the new relative clause. Because it acts as the tool you are working with in the second part of the sentence, it takes the instrumental case (kojom).
Why does the sentence use teško instead of the feminine teška to match the keyboard?
teško isn't describing the keyboard directly here. Instead, it forms the impersonal phrase teško je raditi (it is hard to work). When you describe an action using "it is" plus an infinitive verb, you always use the neuter singular form (which looks exactly like the adverb form).
Why is the verb je placed right after kojom?