Question

car is traveling at constant speed of 20.8 m/s when the car sees sign that is 50.0 meters infront dicides to break the pedal for a constant acceleration of 4.80 m/s2 to reach in a rest mode. What is the cars reaction time?

Answer 1

The distance after he decides to break the pedal

$$d=v^2/(2a)=(20.8)^2/(2(4.8))=45.07 m.$$

The reaction time is

$$t=(50.0-45.07)/20.8=0.237 s.$$