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? a. 4.0 kg • m/s b. 21 kg • m/s c. 47 kg • m/s d. 3900 kg • m/s

The momentum of a moving object is given by:

where
m is the mass
v the velocity of the object

Before the car accident, the driver (of mass m=125 kg) was moving at speed v=31 m/s, so his initial momentum was


However, after the collision the driver is brought to rest: it means his final velocity is zero, and so also his final momentum is zero: . Therefore, the change in momentum of the driver is equal to his initial momentum:

and the correct answer is D.

Efficiency is an action of doing something. for example when you take a test. good efficiency means you did well but bad effeciency or no effiency means you did bad.