1) 공부가 힘들다 : Study is hard.
2) 인생이 힘들다 : Life is difficult.
3) 요리는 힘들다 : Cooking is hard.
1) 수학은 어렵다 : Math is hard.
2) 스마트폰 배우기는 어렵다 : Learning smart phone is hard.
3) 이해하기 어렵다 : Hard to understand.
ㅋㅋ these two word is kinda same. both of them are used in same sentence.
but, 힘들다 means physical difficulty, and 어렵다 means .. emotional difficulty ..