알았다 and 알았어
i was wondering what is the difference between
알았다 and 알았어 ( you know,like at the movie,when the speaker say 알았다 알았다..why not use 알았어?
다했다 and 다했어
and so on..

one more thing,how do you use -ㄴ다 like 걸린다 ? 간다 ?

Question

알았다 and 알았어
i was wondering what is the difference between
알았다 and 알았어  ( you know,like at the movie,when the speaker say 알았다 알았다..why not use 알았어?
다했다 and 다했어
and so on..

one more thing,how do you use -ㄴ다 like  걸린다 ? 간다 ?

Answer

The difference is in speech levels.
There are seven speech levels in Korean, and each level has its own unique set of verb endings which are used to indicate the level of formality of a situation.

알았다 and 다했다 are Haera-che(해라체)
It is used
to close friends or relatives of similar age, and by adults to children
in impersonal writing (books, newspapers, and magazines) and indirect quotations ("She said that...")
in grammar books, to give examples
in some exclamations 
 
알았어 and 다했어 are Hae-che(해체)
It is used
between close friends and relatives
when talking to children

-ㄴ다 is a present ending partile of Haera-che.
So, 걸린다 and 간다 are Haera-che present of 걸리다 and 가다

Refer to http://en.wikipedia.org/wiki/Korean_speech_levels

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