Перед уроком стоит проверить, работает ли проектор.

Here стоит does not mean stands in the literal physical sense.

In the pattern стоит + infinitive, it means something like:

• it is worth ...
• it is advisable to ...
• one should ...

So:

• стоит проверить = it’s worth checking / one should check

This is a very common Russian way to give mild advice or recommendation.

Because the preposition перед normally takes the instrumental case when it means before / in front of.

So:

• урок = nominative
• уроком = instrumental

That is why we get:

• перед уроком = before the lesson

This is a case pattern you simply have to learn with the preposition.

Yes, but the nuance is a little different.

• перед уроком = right before the lesson, immediately beforehand
• до урока = before the lesson, more generally, at some time prior to it

In this sentence, перед уроком sounds very natural because checking the projector is something you would usually do shortly before class starts.

Проверить is perfective, while проверять is imperfective.

Here, проверить is used because the sentence refers to one complete check:

• стоит проверить = it’s worth checking once and making sure

If you said стоит проверять, it would sound more like:

• it’s worth checking regularly
• one should be checking

So the perfective verb fits better here because this is a single practical action before the lesson.

Because работает ли проектор is a subordinate clause.

The main clause is:

• Перед уроком стоит проверить = Before the lesson, it’s worth checking

The subordinate clause is:

• работает ли проектор = whether the projector is working

Russian normally separates this kind of subordinate clause with a comma.

Ли marks an indirect yes/no question. In English, it is often translated as:

• whether
• sometimes if

So:

• работает ли проектор = whether the projector is working

Compare:

• direct question: Проектор работает? = Is the projector working?
• indirect question: проверить, работает ли проектор = check whether the projector is working

In Russian, ли usually comes after the word that is being questioned or focused.

Here the thing being questioned is работает:

• работает ли проектор = whether the projector is working

Putting ли at the very beginning would be wrong in standard Russian.

This is a very common pattern:

• Я не знаю, придёт ли он. = I don’t know whether he’ll come.
• Надо проверить, открыт ли магазин. = We need to check whether the store is open.

Because проектор is the subject of the subordinate clause:

• работает ли проектор = whether the projector is working

The verb работает agrees with проектор, so проектор stays in the nominative.

Russian does not have a separate grammatical form exactly like the English present progressive (is working).

So работает can mean either:

• works
• is working

The exact meaning depends on context.

In this sentence, the natural English translation is:

• whether the projector is working

because we are talking about its current functioning before the lesson.

Yes, in a sense. Russian often uses impersonal constructions where English might prefer an explicit subject.

• Перед уроком стоит проверить... literally has no expressed we or you
• but in meaning it implies something like it would be good to check...

Depending on context, English could translate it as:

• Before the lesson, it’s worth checking...
• Before the lesson, you should check...
• Before the lesson, we should check...

Russian leaves that unstated because it is not important here.

Yes. Russian word order is fairly flexible, though different orders can slightly change emphasis.

For example:

• Перед уроком стоит проверить, работает ли проектор.
• Стоит перед уроком проверить, работает ли проектор.

Both are possible.

The original version sounds very natural because it starts with the time phrase перед уроком, setting the scene first: Before the lesson...

Usually ли is the normal way to form this kind of indirect yes/no question.

So this is standard:

• проверить, работает ли проектор

You can also rephrase it as:

• проверить, работает проектор или нет = check whether the projector is working or not

That version is a bit more explicit. But simply omitting ли without changing the structure would usually sound wrong or incomplete.

It is quite neutral and natural. It would work well in:

• everyday speech
• school or university contexts
• workplace instructions

It sounds a little more polished than a very casual spoken version, but it is not overly formal.

A more direct, conversational alternative might be:

• Перед уроком надо проверить, работает ли проектор.
• Перед уроком нужно проверить, работает ли проектор.

These mean it’s necessary / you need to check and sound a bit stronger than стоит проверить.