머리 잘 잘랐다 vs 머리 자랐다. They both can be correct with a different meaning. 1. 머리(를) 잘 잘랐다 = A) (I/You) have a nice haircut (= They cut it nicely), B) It's a good thing (I/you) had a haircut. * 자르다 = cut, sever. Conjugation irregularly with -아/어, as in 잘라서, 잘라도, 잘랐어, etc ('ㄹ' is added). e.g. 거기를 자르면 안 되고 여길 잘라야 돼. You shouldn't cut it there. Just cut here. 2. 머리(가) 자랐다 = (My/Your) hair has grown long. * 자라다 = grow. Conjugates regularly - 자라서, 자라도, 자랐어, etc. e.g. 너는 자라서 뭐가 되고 싶어? What do you want to be when you grow up? In the case of (1), we can but usually do not include the particle '를'. In (2), it sounds better to include '가'.

But they don't mean the same thing in the first place? 머리 잘 잘랐다 = [someone] cut [someone's] hair well 머리 자랐다 = [someone's] hair grew up 자르다 (잘랐다) = to cut 자라다 (자랐다) = to grow up