Is there a way to make an object like a catapult so that I can stretch and throw it applying a force .Just as in case of angry bird's catapult..Please help me....

check this out in the code exchange..

http://developer.anscamobile.com/code/angry-bird-catapult-simple-pool-example

I havent actually downloaded it, but from the title it seems like it could be what your after :D

Try looking at this:

http://developer.anscamobile.com/code/how-make-angry-birds-catapult