3)A driver take 0.2 second to apply the brake after he see the need for it This is called the raction time of the driver . if the driver is driving with a speed

Question

A driver take 0.2 second to apply the brake after he see the need for it This is called the raction time of the driver . if the driver is driving with a speed of 54km/hr and the brake cause a deceleration of 6.o m/s^2 , find the distance travelled by the car after he see the need to put the brake on .

Answer 1

In the 2 seconds of reaction time, distance traveled = 54km/hr * 2secs = 54000m/3600sec * 2 sec = 30 m

 

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.

 

-2916 = -12s

 

s = 243 m

 

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