"There is an accident in Asia?"
Translation:Có một tai nạn ở châu Á ư?
"Ư", like "hả" and "á", is used to form questions and indicate the surprise of interrogators as well. It's used commonly in writing (and because of being used commonly in writing, it's not only popular in Northern dialects but nationwide).
"Phải không" absolutely can't replace "ư". If you replace "ư" with "phải không", you can still form the question but can't show your surprise.
yes it is. it seems to mean 'yeah', or on this case, 'yeah'? unlike some opinion here, many VN people use this expression (ư) during phone calls (acknowledgement / agreement), and during informal conversation. I was just there in March this year, I understand a bit of language ̣(enough to attend a dinner party with only VN speakers and still have fun - been there 11 times), and I hear 'ư' often.
you probably mean "ừ", not "ư". they are not exactly the same.
when you use "ư", you are surprised to hear sthg and ask if you hear it right.
when you use "ừ", you express agreement to what is said right before.
note that the use of "ừ", as you noticed, is very informal, not to be used with elders (and by elders, I mean anyone a few years and up older than you, not only elderly people), bosses, teachers, strangers, otherwise you would sound rude.