I am trying to create the rubber band type or elastic rope.
i ant to do something like bellow link. http://heyalda.com/smash-turtle/
No one will write the code for you so I think you would be hard up getting an answer. Luckily for you I searched for a tutorial for creating rope with box2d and cocos2d on google and found this really good tutorial on making a cut the rope type game
EDIT: iPhone game "climbers" https://github.com/haqu/climbers
It isn't exactly what you want. However, I'm sure this is a lot better than what you have now :)