How to open a door in two easy steps: Build up speed. Hit it.
When opening door a door this way, you should try to hit with three points of your body at the same time to reduce the impact shock: the side of your thigh, the side of your hip and the back of your shoulder.
This allows you to open a range of different doors without severe bodily harm. Unfortunately it is impossible to say generally if the lock or the hinges will give in first.
Wait, you wanted to open an unlocked door? Never mind.