Question

A car moving along a straight highway with speed
144 km/h is brought to stop within a distance of
400 m with uniform retardation. How long does it
take for the car to stop?
(1) 10 s
(3) 20 s
(2) 15 s
(4) 25 s
​

Answer 1

Answer:

correct answer is (3) 20 s

Explanation:

Given,

u=144 km/h = 40 m/s

v= 0 m/s (as the car stops)

distance covered before stopping (s) = 400 m

Using 2 as = v²- u²

2*a*400= 0²-40²

800a = -1600

a= -1600/800

a= -2 m/s²

Now, time taken to come to a stop (t) = v-u/a

(Since a=v-u/t)

t= 0-40/-2

= -40/-2

= 20 s

HOPE IT HELPS!!!