The driver of a blue car moving at a speed of 80km/hr suddenly realises that she is about to rear-end a red car moving at a speed of 60 km/hr. To avoid a collision what is the maximum speed the blue car can have just as it reaches the red car?
peed of the car moving ahead = 60 km/hr
Speed of the car moving behind = 80 km/hr
Let the speed required of the car moving behind at the time it reaches the car moving ahead be x km/hr
Now the relative velocity of the car moving behind wrt the car moving ahead shud not be positive.
x - 60 <= 0
x <= 60
as the question asks for the maximum value of x ..
hence ..answer is 60 km/hr.