Она смогла удержать тяжёлую дверь.

Because the subject is она (she), and Russian past-tense verbs agree with gender and number.

• смог = masculine singular past
• смогла = feminine singular past
• смогло = neuter singular past
• смогли = plural

So:

• Он смог = He managed
• Она смогла = She managed

The -ла ending is the key sign that the subject is feminine.

Смогла is the past tense of смочь, which means to be able to, to manage to, or to succeed in doing something.

In this sentence, она смогла удержать means:

• she was able to hold
• she managed to hold
• she succeeded in holding

It often suggests that the action was difficult, but she succeeded.

This is a very common question.

• могла = could / was able to in a more general sense
• смогла = managed to / succeeded in a specific situation

So:

• Она могла удержать дверь can mean She could hold the door (she had the ability)
• Она смогла удержать дверь means She managed to hold the door (she actually succeeded)

In this sentence, смогла emphasizes the successful result.

Because after смочь (to manage / to be able), Russian normally uses an infinitive.

Structure:

subject + смог/смогла + infinitive

So here:

• Она = she
• смогла = managed
• удержать = to hold / to keep / to hold back

Literally, the structure is something like She managed to hold.

Other examples:

• Он смог прийти = He managed to come
• Мы смогли закончить = We managed to finish

Удержать usually means to hold back, to keep from moving, to keep under control, or to keep hold of.

With дверь (door), it means something like:

• to hold the door
• to keep the door from opening / swinging
• to keep control of the door

So this is not just the basic idea of physically holding something in your hands. It suggests preventing it from moving or managing to keep it in place.

Because удержать and держать are related, but not identical.

• держать = to hold in a general, ongoing sense
• удержать = to hold back / keep hold of successfully, often with a result

Compare:

• Она держала дверь. = She was holding the door.
• Она смогла удержать дверь. = She managed to hold the door / keep it from moving.

Also, удержать is perfective, which fits well with смогла because the sentence focuses on a successful completed result.

Russian aspect is very important here.

• удержать = perfective
• удерживать = imperfective

The perfective form is used because the sentence talks about a successful completed achievement: she managed to do it.

This pairing is very natural:

• смогла удержать = managed to hold successfully

If you used the imperfective, it would usually change the meaning or sound less natural in this context.

Because дверь is the direct object, so it is in the accusative case.

The dictionary form is:

• тяжёлая дверь = heavy door

But after a transitive verb like удержать, the object goes into the accusative:

• тяжёлую дверь

For feminine singular adjectives:

• nominative: тяжёлая
• accusative: тяжёлую

So the adjective changes to match the noun’s case.

Because дверь is a feminine noun of the third declension, and in the singular its nominative and accusative forms are the same.

So:

• nominative: дверь
• accusative: дверь

This is normal for many inanimate nouns, though the exact pattern depends on the declension type.

The adjective still changes:

• тяжёлая дверь → nominative
• удержать тяжёлую дверь → accusative

Yes, Russian word order is flexible.

The neutral order here is:

Она смогла удержать тяжёлую дверь.

This sounds natural and straightforward: She managed to hold the heavy door.

But you can move words around for emphasis, for example:

• Тяжёлую дверь она смогла удержать.
  Emphasis on the heavy door
• Удержать тяжёлую дверь она смогла.
  Emphasis on the fact that she did manage it

Even though word order can change, the cases and verb forms still show the grammatical relationships.

Russian has no articles like a or the.

So дверь can mean:

• a door
• the door

The exact meaning depends on context.

In this sentence, English will usually translate it as the heavy door or a heavy door depending on the situation, but Russian does not mark that distinction with an article.

тяжёлую is pronounced roughly like:

tya-ZHO-lu-yu

The stress is on ё:

• тяжёлую

Important points:

• ё is always stressed when written
• it sounds roughly like yo
• in normal Russian writing, ё is often replaced by е, so you may also see тяжелую

But the correct pronunciation is still with ё:

• written casually: тяжелую
• pronounced: тяжёлую

It can be translated in a few ways, depending on context.

Possible translations:

• hold the heavy door
• keep hold of the heavy door
• hold back the heavy door
• keep the heavy door from opening / moving

The Russian verb удержать often carries the idea of successfully keeping something under control. So the best English choice depends on what the door was doing:

• if it was trying to swing open: hold back
• if it was hard to keep shut: keep closed
• if she simply kept it in place: hold

They are:

• она = she
• смочь = to be able, to manage
• удержать = to hold back, to keep hold of
• тяжёлый = heavy
• дверь = door

The sentence uses changed forms:

• смогла ← from смочь
• тяжёлую ← from тяжёлый

Learning to recognize dictionary forms helps a lot when reading Russian.