Question

a driver takes 0.20 second to apply the break after he sees a need for it. this is called a reaction of time of the Driver. if he is driving a car at a speed of 84 km per hour and the brakes colloidal solution of 6.0 metre per second square, find the distance travelled by a car after he sees the need to put the brakes on?

Answer 1

The car is moving at speed of 54 km/hr i.e., 15 m/sec

that is initial speed after applying brakes is (u) = 15 m/sec

say at point A, he sees the need to put brakes

at point B, he puts brakes and then car starts deceleratin

at point C, car finally comes to rest

from A to B it moves with speed of 15m/sec in 0.2 sec

so distance covered is S1 = v.t = 15*0.2 = 3 mts

from B to C it moves with constant deceleration of -6 m/sec2 and initial speed of 15m/sec

Using relation V2 - u2 = 2*(-a)*S

S2 = V2/2*a = 15*15 /(2*6) =18.75 mts

the distance travelled by car after he sees need to put brakes is S1+S2

= 21.75 mts ( nearly 22 mts)