When a student's grades hit bottom it is time to hit the books.

VOA: special.2009.09.20

Something that has hit bottom can go no lower.

VOA: special.2009.09.20

Another expression involving hit is hit bottom.

VOA: special.2009.09.20

he said, "hit it good and hard, so we will all go to the bottom."

VOA: special.2010.06.17