Question

A driver takes 0.20 s to apply the brakes after he sees a need for it. This is called the reaction time of the driver. If he ils driving a car at a speed of 54 km/h and the brakes cause a deceleration of `6.0 m/s^2`, find the distance travelled by the car after he sees the need to put the brakes on.

Answer 1

Correct Answer - B
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`.