tense

[Helen111]

Are both sentences acceptable/correct?

Nobody knows why the bridge has collapsed?

Nobody know why the bridge collapsed?

If not what is the difference, can we use the perfect tense, considering the fact that the bridge will not collapse anymore?

[udara sankalpa]

Hi there
I'm not a native speaker or teacher, but would like to add the follwoing:

-Nobody knows how the bridge has collapsed. (Bridge has not yet been rebuilt)

-Nobody knows how the bridge collapsed. (Probably it's been rebuilt)

This is just how I feel, please correct me if I'm wrong.

cheers
Udara

[Helen111]

Thank You very much for the quick reply, I should have thought about it as well but sometimes I choose the easy way to get an answer.

Have a nice day kind regards Helen Czipa from Hungary

[Anglika]

Are both sentences acceptable/correct?

Nobody knows why the bridge has collapsed?

Nobody know why the bridge collapsed?

If not what is the difference, can we use the perfect tense, considering the fact that the bridge will not collapse anymore?

No question marks are required - these are both statements that it is not known for what reason the bridge collapsed.

Both are acceptable and mean much the same. Whether the bridge will collapse again is irrelevant.