Hun falt på rumpa.

Because falt is the past tense of falle (to fall).

• å falle = to fall
• faller = falls / is falling
• falt = fell
• har falt = has fallen

So Hun falt på rumpa is in the past: She fell on her bottom/butt.

The infinitive is å falle.

This is an irregular verb, so the forms are not built in a completely regular way:

• å falle = to fall
• faller = fall / falls
• falt = fell
• har falt = have/has fallen

A learner often has to memorize falt as the past form.

Hun is the subject pronoun meaning she.

In a basic Norwegian main clause, the normal word order is:

Subject + verb + rest

So:

• Hun = she
• falt = fell
• på rumpa = on her bottom/butt

That makes the sentence structure very straightforward.

På is the preposition on / onto, and rumpa is the definite form meaning the butt / the bottom.

In this sentence, falle på + body part is a natural way to say someone landed on that part of the body.

So på rumpa means something like:

• on her bottom
• on her butt

It is the natural idiomatic phrasing here.

Norwegian very often does not use a possessive with body parts when the owner is obvious from the subject.

So instead of saying the equivalent of She fell on her bottom, Norwegian simply says:

Hun falt på rumpa.

This is very common with body parts and clothing. The context already tells us whose bottom it is.

Yes, rumpa is a very normal, everyday word. It means the bottom / the butt.

It is somewhat informal, but not especially rude. It can sound:

• casual
• everyday
• a bit child-friendly in some contexts

Depending on context, Norwegian also has other words, for example:

• bak / baken = backside / rear, often milder or more neutral
• ræva = much more vulgar

So rumpa is a common and natural choice in an everyday sentence.

Both can exist, but rumpa is very common in everyday Norwegian.

In Bokmål, many nouns can appear with either:

• -a definite ending
• -en definite ending

depending on style, gender treatment, and usage.

So you may see:

• ei rumpe – rumpa
• en rumpe – rumpen

In practice, rumpa sounds very natural and colloquial in a sentence like this.

Yes, it is completely natural.

It sounds like a normal everyday sentence describing that someone fell and landed on their bottom.

A very similar and also common alternative would be:

• Hun datt på rumpa.

That uses datt, the past tense of å dette (to fall), which is also very common in speech.

Both can often be translated as fell, and in many everyday situations they overlap.

Very roughly:

• falt comes from å falle
• datt comes from å dette

In real usage, many Norwegians use both in similar contexts.
Hun falt på rumpa and Hun datt på rumpa can both sound natural.

For a learner, the important thing is:

• falt is correct
• datt is also very common in speech

A simple approximate pronunciation for an English speaker is:

hoon falt paw ROOM-pah

A few notes:

• Hun sounds like hoon, not like English hun.
• falt has a clear t at the end.
• på has a long vowel, roughly like paw.
• rumpa is stressed on the first syllable: RUM-pa.

The exact pronunciation varies by dialect, but this approximation is good enough for many learners.

Yes. In natural English, both ideas are very close here.

The Norwegian sentence mainly tells you the result of the fall: she ended up landing on her bottom.

So depending on context, you might translate it as:

• She fell on her butt.
• She fell onto her butt.
• She landed on her bottom.

All of these can fit the sentence well.