Question

A driver takes 0.2s to apply the brakes after he sees a need for it. This is called the reaction time for the driver. If he is driving car at a speed of 54 km/h and brakes causes a retardation of 6 ms-2, find distance traveled by the car after he sees the need to put brakes.

Answer 1

Hey

▶In the 2 seconds of reaction time, distance travelled = 54km/hr × 2secs

= 54000m/3600sec × 2 sec = 30 m(since Distance =speed ×time)

 ▶Once he brakes, assuming constant deceleration, Apply Newton's Third Law of Motion:

 
${v}^{2} - {u}^{2} = 2as$

0^2 - 54^2 = 2* -6 * s      Final speed is zero on coming to rest.

 
${0}^{2} - {54}^{2} = 2 \times - 6 \times s \: (final speed is zero on coming to rest).$
-2916 = -12s

 s = 243 m

▶Total distance traveled after realizing the need to brake = 30m + 243m = 273m.


Hope it helps to you.

Thanx