A driver takes 0.20 second to apply the brakes (reaction time). If he is driving car at a speed of `54kmh^(-1)` and the brakes cause a deceleration of `6.0ms^(-1)`? Find the distance travelled by car after he sees the need to put the brakes.

Explanation

In reactiion time the body moves with the speed of 54 km/hr = 15m/sec (constant speed).
Distance travelled in this time,
`S_1=15xx0.2
=3m
When breades are applied
u=15 m/s
v=0
a=-6m/s^2(deceleration)
S_2=(v^2-u^2)/(2a)
=(0-15^2)/(2(-6))
=18.75m
Total distance = S_1+S_2
=3-18.75+21.75m
= 22m`.