It is a noun. So you could say "It is impossible to survive a 5,000 foot fall".
I can give you several sentences.This is an impossibly hard problem.He had an impossibly long list of complaints.Her impossibly upbeat personality finally cracked, and we saw her dark side.
"Iron Man flew impossibly high with the help of his suit."
impossibly she tried to sculpt the ice sculpture without practice.
That would be impossibly hard.
impossibly
5 syllables
There apparently is no Impossibly Hard Quiz 4 (as of 2011).(See the related questions for the first three quizzes.)
That score is impossibly high.
Edward Cullen from twilight
i do not know how to use embalming in a sentence. (there is the sentence)
The Phoenicians use the sea for trade because the alternative - slow 1 ton carts was impossibly over distances greater than 60 km, and their trade distances were in 1,000s of km.
So- you are asking when to use 'when' in a sentence. When you are asking how to use when in a question, you are already using when in a sentence, because a question actually is a sentence. I like to use when in a sentence whenever I like.