3.6 A car moving along a straight highway with speed of 126 km h–1 is brought to a stop within a distance of 200 m. What is the retardation of the car (assumed uniform), and how long does it take for the car to stop ?


:Initial velocity of the car, u = 126 km/h = 35 m/s

Final velocity of the car, v = 0

Distance covered by the car before coming to rest, s = 200 m

Retardation produced in the car = a

We know that,
v2-u2=2as
(0) -(35)2=2×a×200
a=-35×352×200=-3.06 m/s2
Using,
v=u+at
t=v-ua=0-35-3.06=11.44s