Question

Two cars are driving at the same constant speed on a straight road, with car 1 in front of car 2. Car 1 suddenly starts to brake with constant acceleration and stops in 10 m. At the instant car 1 comes to a stop, car 2 begins to brake with the same accelaration. It comes to a halt just as it reaches the back of car 1. Whar was the separation between the cars before they started braking?

Answer 1

the average speed during braking is half of the constant driving speed

so car 2 travels 20 m in the time it takes car 1 10 m to stop
... this moves car 2 10 m closer to car 1

car 2 then travels an additional 10 m while stopping