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 is driving at a speed of 54km/h and the brakes cause a deceleration of 6.0m/s^2, find the distance travelled by the car after he sees the need to put the brakes.

(a) 18.75m

(b) 225 m

(c) 21.5 m

(d) 12 m

The question was asked in an online quiz.

This is a very interesting question from Motion and Mechanics topic in chapter Advanced Engineering Materials of Engineering Physics II

Answer 1

Right option is (c) 21.5 m

The explanation: Distance covered in 0.20s = 15 × 0.20 = 3 m

For motion with deceleration:

U = 15m/s v = 0 a = -6 m/s^2

As v^2 – u^2 = 2as

s = 18.75 m

Total distance travelled = 3.0 + 18.75 = 21.75 m.