A driver of car takes `-20 s` (which is the reaction time of dricer ) to apply the brkes after he sees an obstruction at a distance of `25 m` from him . If he is driving car at a speed of `54 km h^(-1)` and the brakes cause a deceleration of `6.0 km h^(-2), predict whether he will avert collistion or not.

Explanation

Here, reaction time `=0.20 s,
During the time of reaction,the car contiuous to move with uniform speed of `54 km h^9-1) =15 ms^(-1)`
Distance coverd by car in time `0.20 s`
`=15 xx 0.2 =3.0 m`
Taking motion of car when brake is applied and its velcity becomes zero . Then
`u=15 ms^(-1), a=- 6.0 ms^(-2), v=0, S=?`
`v^(2) =u^(2) + aS`
or `S=(v^(2) -u^(2))/(2a) = (0- (15)^(2))/(2(-6)) =18 .75 m`
Total distance travelled by car `=3.0 +18 .75`
`=21. 75 m`
As this distance is less than `25 m`, so the driver will avert the collision.