Simple mobile car damage

I’m making a mobile game, and (you guessed it!) it contains cars.
I was wondering how I would make some simple car damage, for example, when the car hits something the hood flaps open, etc. Should I make the car hood another model and attach it to the car? Or is there some kind of bone system?

The least performance consuming and most realistic would be to replace meshes as you crash. You can do this by placing all damage game objects in the scene and disabling and enabling them as per your requirement. To add extra realism, like the hood and doors flap while driving (like in GTA), you can attach hinge joints to meshes. Or you can use a mesh deform system like this one:

http://forum.unity3d.com/threads/50214-NOW-WITH-SOURCE-Mesh-deformation-on-impact

But this method doesn’t look that realistic and can be CPU expensive. The best method would be to use mesh replacement with hinge joints. You can even set break forces to hinge joints with which you can create flying doors, etc. after a crash.