Question

A driver takes 0.2 s to apply the brakes after he sees a need for it. This is called the reaction time of of the driver. If he is driving a car at a speed of 54 km/h and the brakes cause a deceleration of 6.0 m/s², find the distance traveled by the car after he sees the need to put the brakes on. Concept of Physics - 1 , HC VERMA , Chapter "Rest and Motion : Kinematics

Answer 1

Solution:
Initial velocity=u=54km/h=54x5/18=15m/s
time=t=0.2sec
Final velcoity=v=0m/s
deceleration =a= 6m/s2

Now, Distance travelled by car during reaction time : 
Distance=Speedx time
Distance=15x0.2
=3m

From third equation of motion:
v²-u²=2as
0²-15x15=2x-6xs
s=-15x15/-12
S=225/12a
s=18.75m 

So the total distance travelled by the driver after  he seeds the need to put the brakes ON= 18.75+3=21.75m

Answer 2

Answer:

Answer is 21.75m/s

Explanation:

The need of putting break is 18.75m and distance is 3m so add it and the answer will definitely come!