During a car accident, a 125 kg driver is moving at 31 m/s and in 1.5 seconds is brought to rest by an inflating air bag. what is the magnitude of the change in momentum of the driver?

Momentum = (mass) (speed)

The driver's initial momentum is (125 kg) (31 m/s) = 3,875 kg-m/s

At rest, his momentum is zero.

The change in his momentum is  (0 - 3,875 kg-m/s)  =  - 3,875 kg-m/s .

The average force exerted on him by the airbag is

                          (3,875 kg-m/s) / (1.5 s)

                     =        2,583.333... kg-m/s²

                     =         2,583.333... newtons   (about about 581 pounds)

That's what it takes to stop a 125 kg mass moving at 31m/s in 1.5sec.

The negative acceleration is    31/1.5 m/s² = about

                                                   =  20.333... m/s²  =  about  2.1 'G's.

If he were not wearing his seat belt and the airbag did not deploy,
then he would not be brought to rest ... at least not until he hit the
windshield at 31 m/s ... about  69.3 mph .

              

Wind or electric energy force force of friction

Answer(a)   the matererials that are in contact, the two materials and the nature of their surfaces/// (b)/// the force pushing the two surfaces together, pushing the surfaces together causes the more of the asperities to come together and increases the surface area in contact with each other