a boy was sleeping and girl forced him to hav sex but the boy was not ready for it ...is it a sin?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

The boy whom you mentioned in the question should repent to Allaah as he has no excuse for fornicating with the pretext that the woman forced him to do so. Many scholars are of the view that it is impossible to imagine being forced to commit Zina (fornication or adultery); and this is the view of Ahmad and Abu Haneefah .

For more benefit, please refer to Fatwa 89882.