The correct option is B 8 m/s2
As per the question, final velocity of the car will be v=0
Given, initial velocity u=40 m/s, distance s=100 m
As per 3rd equation we have
v2−u2=2as
⇒ 0−402=2a×100⇒ a=−1600200=−8 m/s2
Thus, the retardation of the car is 8 m/s2