What's the difference between 打开 and 开门?

Question

How can I tell when to use `打开` and when to use `开门` in Chinese? For example, in the following sentences: * 这扇门打开了 * 这个书店开门了 Why does the first sentence use `打开` and the latter use `开门`? Also, is it necessary to use `了` in this sentence?

Answer 1

Shan J. is right; but 商店开门了 means the shop has opened (for business that day), the shop is open; this is a more figurative sense of the VO compound whose literal meaning is to open the door.

Answer 2

打开: open sth.

EX: 打开一本书 open a book

EX： 打开一个罐头 open a can

EX: 这扇门打开了 The door is (already) open.

开门= 打开门：open the door 【门 is “door”】

*When a verb + ”了" means something already happened. It shows past tense.