Question

car is moving with speed u driver of the car sees red traffic light his reaction time is t then find out the distance travelled by the car after the instant when the driver decided to apply brakes assume uniform retardation 'a' smaller after applying brakes

Answer 1

By using the Newton laws F= m*g so a+=-µ*g,  ut+u^2/2a, hence the T brake = average speed * tbrake.  

By using the above formula the student enter the value and apply to find out answer without meeting any trouble of it.

In case of any doubt, the student can get right ides to apply and get answer.

Answer 2

D1 is the distance covered in motion before applying breaks

And D2 is distance covered in retardation