"Are you at work?"
Translation:Ты на работе?
What I want to know is, what's the system for deciding how new loan words get either «в» or «на».
Вы is for formal situations (Вы) and plurality (вы) while ты is for informal situations when it's one person. If you don't know which to use, use "вы" :) "вы" is like "vous" (French) and "sie" (German) while "ты" is like "tu" (French) and "du" (German).
I am a beginner in Russian, but I think it is because of the case. The word declines because of the preposition.
"Ты в работе" = " ты работаешь" = you are working.
"Ты на работе" = you are at work.
but the 1st sentence is informal and used rarely
"в работе" also means "work in progress." Like, "Этот проект сейчас в работе" - "This project is currently in work"
So, "Ты в работе" also has a meaning of "You're under construction" - a thing that a soon-to-be father would say addressing his pregnant wife's belly (or rather the guy shaping up in there).