Too heavy doors? - Hinge joint doesn't work

Hi, i have created the doors, and tried to use hinge joints, i used this tutorial as a guide
http://www.youtube.com/watch?v=f4xikqJdkwM

It works, but i have to add a lot of forcePower to open the door. somebody knows, why?
http://tinypic.com/r/34rgcvt/8
Look on force amount
thanks everyone.