Learn Polish: Mechanik musi rozebrać silnik. - The mechanic must dismantle the engine.

The base verb is brać (to take). The prefix roz- (which becomes roze- here to make it easier to pronounce) adds the idea of separation or undoing. So, taking something apart piece by piece gives us rozebrać, meaning to dismantle.

I previously learned that rozebrać się means to get undressed. Is this the exact same verb?

Yes! Getting undressed is essentially dismantling your outfit. When used with the reflexive pronoun się, it means to undress. When used without się and followed by a direct object like silnik, it means to physically take an object apart.

Why does silnik look like it is in the nominative case if it is the object being dismantled?

It is actually in the accusative case because it is the direct object of the verb. However, because silnik (engine) is a masculine inanimate noun, its accusative form looks exactly the same as its dictionary (nominative) form.

Why do we use the perfective verb rozebrać instead of its imperfective form rozbierać after musi?

When using modal verbs like musi (must), we choose the perfective infinitive when the goal is a finished, single action. The mechanic needs to completely take the engine apart, not just engage in the continuous process of dismantling it.