The momentum of a moving object is given by:
[tex]p=mv[/tex]
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
[tex]p_i = mv=(125 kg)(31 m/s)=3875 kg m/s \sim 3900 kgm/s[/tex]
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: [tex]p_f=0[/tex]. Therefore, the change in momentum of the driver is equal to his initial momentum:
[tex]\Delta p = 3900 kg m/s[/tex]
and the correct answer is D.
