Breakdown of Мой друг читает эту книгу, чтобы поступить в институт.
книга
book
друг
friend
мой
my (мой, моя, моё) / mine
этот
this [f: эта, n: это]
Questions & Answers about Мой друг читает эту книгу, чтобы поступить в институт.
Why do we use the infinitive поступить right after чтобы?
Because the subject is the same in both halves of the sentence. Your friend is the one reading, and your friend is the one who wants to enroll. When the person doing both actions is the same, Russian uses чтобы followed by an infinitive, which translates well to 'in order to'.
Could we use the imperfective verb поступать here instead?
You could, but it changes the meaning slightly. поступать focuses on the process of applying or taking entrance exams. By using the perfective поступить, the sentence emphasizes the actual goal: successfully getting accepted and enrolling.
Why is it в институт (accusative) and not в институте (prepositional)?
Even though we say 'in the institute' in English, the verb поступить implies entering into a place or a new status. Because it describes a direction or a transition rather than a static location, it requires the accusative case (в институт).
I see эту книгу is in the accusative case. Why did both words change?
книга changes to книгу because it is the direct object receiving the action of reading. In Russian, pointing words like эта (this) must match the case of the noun they describe. So, the feminine nominative эта becomes the accusative эту to match книгу.