At one filling station there was a Chryslus Rocket 69 that I bumped into. It was set up to look like the station was filling the car when the bombs fell.
To cut a long story short, the bumping caused the car to start vibrating like mad and then when I was laughing at it the thing pinged off into air, came back down and started bouncing around like a balloon.
Yup... basically every car has really low mass.
Another time a BoS vertibird got shot down and the wreckage bounced all over the place but don't affect the game world. I thought that one time I had got hit by another crashed vertibird but now I think it was probably a mini nuke going off.. Because these wrecks don't affect you it removes a whole load of immersion in the game. It's like the falling parts are actually holograms.