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.