Reaction time : the lapse of time between stimulation and the beginning of response.
You are driving on the high way and listening to the music you like most.
Suddenly, you see that the brake light of the car in front of you just came on.
You try to hit the brake and slow down your car.
But, there is a small time delay between the time that you first see the brake light of the car in front of you and the time that you step on the brake. This is your reaction time.
During that period of time, your car is still moving at the same HIGH speed!
What is minimum distance that you must maintain between front of your car and the rear of the car before yours if you do not want something VERY BAD happened?
If both cars need the same distance to fully stopped (why is this relavant?), the minimum distance is
( the velocity of your car )* ( your reaction time )