Impusle, momentum and collisions

1. In a car collision, the driver's body changes speed from a high value to zero. This is true regardless of whether an airbag is used, so why use the airbag? How does it reduce injuries?

2. You want to close an open door by throwing either a 400 g lump of clay or a 400 g rubber ball toward it. You can throw either object with the same speed, but they are different in that the rubber ball bounces off the door while the clay just sticks to the door. Which projectile will apply the larger impulse to the door (and therefore be more likely to close it)?