Cuando termine la obra, vamos a aplaudir.

Because after cuando when you are talking about a future event that has not happened yet, Spanish normally uses the present subjunctive.

So:

• Cuando termine la obra, vamos a aplaudir. = When the play/performance is over, we’re going to applaud.
• Cuando termina la obra, aplaudimos. would usually describe a habit or something that normally happens: When the play ends, we applaud.

So termine is not past tense here. It is present subjunctive, used because the ending of the performance is still in the future.

Because cuando can be followed by either:

• the indicative, if the action is seen as real, habitual, or already known
• the subjunctive, if the action is in the future or has not yet happened

In this sentence, the ending of the performance has not happened yet, so Spanish treats it as pending/future:

• Cuando termine la obra... = future, not yet completed

Compare:

• Cuando termina la obra, la gente sale.
  When the play ends, people leave.
  → habitual/general truth

• Cuando termine la obra, la gente saldrá.
  When the play ends, people will leave.
  → future event

Obra has several meanings, so learners often wonder about it.

Common meanings include:

• play / theatrical work
• work / piece of art
• building work / construction

In this sentence, because of vamos a aplaudir (we are going to applaud), the most natural meaning is probably:

• the play
• the performance
• possibly the show

So la obra here most likely refers to a performance ending, after which the audience applauds.

Both are possible, but they are slightly different in style and feel.

• Vamos a aplaudir = we’re going to applaud
• Aplaudiremos = we will applaud

In everyday spoken Spanish, ir a + infinitive is very common and often sounds more natural and conversational, just like English often prefers going to over will.

So:

• Cuando termine la obra, vamos a aplaudir. sounds very natural in speech.
• Cuando termine la obra, aplaudiremos. is also correct, but can sound a bit more formal or simply more like the simple future.

Because they come from two different things:

• vamos a = the structure ir a + infinitive, meaning to be going to
• aplaudir begins with the letter a

So the sequence is:

• vamos
  • a
    • aplaudir

This is completely normal in Spanish. The two a sounds are both pronounced; they are not merged in writing.

Yes. Spanish often leaves out subject pronouns because the verb ending already shows who is doing the action.

In this sentence, vamos clearly means we go / we are going, so nosotros is unnecessary.

You could say:

• Cuando termine la obra, vamos a aplaudir.

or

• Cuando termine la obra, nosotros vamos a aplaudir.

The second version adds emphasis, for example if you want to stress we specifically.

Because the sentence begins with a subordinate clause:

• Cuando termine la obra = When the play ends

Then comes the main clause:

• vamos a aplaudir = we’re going to applaud

In Spanish, when this kind of time clause comes before the main clause, a comma is commonly used:

• Cuando termine la obra, vamos a aplaudir.

If the order is reversed, the comma is usually not used:

• Vamos a aplaudir cuando termine la obra.

Yes. That is also correct.

Both are possible:

• Cuando termine la obra
• Cuando la obra termine

The meaning is the same. The difference is mainly word order.

Cuando termine la obra is probably the more neutral and common order in this case.
Cuando la obra termine may sound a little more deliberate or slightly more literary, depending on context.

Sometimes yes, but the meaning changes slightly.

• Cuando termine la obra = when the play ends / when the performance finishes
• Cuando se termine la obra can suggest when the play is finished, and in other contexts may sound more passive or may imply completion of something being carried out

With obra meaning play/performance, termine is the most straightforward choice.

If obra meant construction work, then se termine la obra would be very common:

• Cuando se termine la obra, abrirán la calle.
  When the construction is finished, they’ll reopen the street.

So the best option depends on what obra means.

Not always. Aplaudir can be used:

• without an object: aplaudir = to applaud
• with a direct object: aplaudir a alguien / algo = to applaud someone / something

Examples:

• Vamos a aplaudir. = We’re going to applaud.
• Vamos a aplaudir a los actores. = We’re going to applaud the actors.
• El público aplaudió la obra. = The audience applauded the play.

In your sentence, no object is needed because the focus is simply on the action of applauding.

Grammatically, yes, but context matters.

Because obra can mean work, that translation is possible in isolation. But the verb aplaudir makes a performance-related meaning much more likely. People normally applaud:

• a play
• a show
• a performance
• the actors

So the most natural interpretation is probably:

• When the play/performance is over, we’re going to applaud.

Not in this sentence.

• acabé = I finished → wrong person and wrong tense
• acabará = it will finish → Spanish normally does not use the future tense after cuando for this kind of future time clause

Spanish prefers:

• Cuando termine la obra...
• Cuando acabe la obra...

Both termine and acabe are good subjunctive forms here.

So a very close alternative is:

• Cuando acabe la obra, vamos a aplaudir.

Yes. Terminar is a regular -ar verb.

Its present subjunctive forms are:

• yo termine
• tú termines
• él/ella/usted termine
• nosotros/nosotras terminemos
• vosotros/vosotras terminéis
• ellos/ellas/ustedes terminen

So in Cuando termine la obra, termine agrees with la obra because la obra is third person singular.