-네 is an ending to describe something you've just noticed with slight admiration. Hence, it leads the listener to say "yes" or to respond to you whatever the listener thinks about it. I wouldn't expect my friends to say yes or anything else after saying the two, 나 밥 먹었네 and 나 잠 많이 잤네. They would probably say "그래서 어쩌라고? So what?" A : 나 숙제 안 했는데, 넌 했어? B : 미안하지만 난 숙제 했네. ㅋㅋ (teasing A indirectly) -네 can be used as an ending to describe something in general like -어, but in this case -네 sounds classical(old-style/boring to young people).