In the following link you have a nice blog with a very good explanation about the different ways to express the idea of “quedarse” in English: http://miprofedeinglesvillajoyosa.wordpress.com/clases/quedar-vs-to-be-to-have-to-stay-etc/
But I’m going to focus on the difference between Stay/ Be as the question appeared in class, and thus I’m copying the explanation here:
1- ‘to stay’ = hospedarse, es decir se usa para hablar de hospedarse en un sitio.
Q: Where did you stay while you were in Shrewsbury? A: I stayed with my cousin.
Q: Did you stay in the ‘Ritz’ when you were in London? A: No, I didn’t. I stayed in a ‘bed and breakfast’ in Earl’s Court.
2- ‘To stay’ = quedarse, permanecer, en el sentido de quedarse en un sitio sin irse a otro. In this sense, ‘to stay’ means the opposite of ‘to leave’.
Examples: I stayed in London for ten days.
She stayed at home all weekend.
I’m staying here a few more days, but then I’m leaving for Bristol.
Stay/wait here for a minute. I’ll be back.
Como mucha gente ha aprendido que stay debería traducirse como estar, cuando tienen que preguntar cosas como “Dónde estuviste?” lo intentan poner. Muy mal! Lo correcto es:
¿Dónde estuviste? = Where were you?
stay calm = mantener la calma
stay strong= sé fuerte
stay up = not go to bed (late at night) = no acostarse (y mantenerse despierto).
stay in = quedarse en casa