can he hurt her

my 7 month old male gets over the 5 month old female and tries to have sex - i guess - with her. she had been spayed a month ago. although she won't let him from what i've seen she screams and grouls at him, incase he does can he hurt her.

If your male is still intact, it is conceivable that he will hurt the kitten. If you can seperate them for awhile and introduce them gradually together that will help. But if you male is neutered then it is a case of him showing her who is Alpha, although what you have described is a bit sexually aggressive for a neutered male.

I've read that cats have "barbs" on the end of their penises, and when they pull out of a female it tears their vagina and this hurts.

If your male is not neutered, then it really is best to have him fixed immediately!

I think the barb thing is with big cats like tigers and lions.

I am sure the large cats have barbs, but domestic males have them as well. It ensures that the sperm is released and gets to where it's going before the female gets angry and pulls away.