I bought an accord 92 and the alternator belt seemed in good condition but after one week drive , its was torn, i was wondering what caused it? is it because the belt was too tight, or the belt was old? what could be other reasons

 

so you bought a used car, did the previous owner tell you how long it had been since the belt had been replaced? Chances are, the belt was probably just in need of being replaced. But just do a visual inspection and make sure nothing is protruding into or towards the area in which the belt travels. If you don't see anything, then it's most likely just an old belt. Replace it and watch it for signs of something rubbing it or any other premature wear.

 

well the belt has been replace and whenever i start the car , the belt makes a shrieking sound , and then it never happens until i start the car again,, is it possibly because the belt is loose or the belt is too tight may be?

 

From time to time a new drive belt needs to be retighten after a short time after installation. This may be what you're running into since the alternator works like he...k right after startup trying to recharge your battery.
Now might be a good time to check your other belts as well. One, or more of the others may require attention also.

P