Question

A driver takes 0.2 s to apply brakes. If he is driving at a speed 54km/hr and the brakes cause a deceleration of 6m/s^2 find the distance travelled by the car,after he sees the need to apply brakes

Answer 1

54km/h = 15m/s

S1 = ut
= 15 * 0.2
= 3 m

S2 = u^2 / (2a)
= (15)^2 / (2 * 6)
= 225/12
= 18.75 m

S = S1 + S2
= 3.0m + 18.75m
= 21.75 m

Answer 2

Speed = 54km/h =
15m/s
time = 0.2Sec

We know that

S= ut

S1= 15 × 0.2

u = 3m

S2 = u² / 2 a )

= 15² / 2 × 6

= 225/ 12

= 18.5

S = s1 + s2

= 3 + 18.75

= 21.75m