Car 1 started at rest and coasted toward the intersection from the top of a 50-meter hill.
Car 2 was on a flat stretch of road at the bottom of the hill in front of Car 1.

At the bottom of the hill, before braking, Car 1 was going 30 m/s and Car 2 was going 20 m/s.
From the skid marks on the road you can see that Car 1 applied force on its brakes for 5 seconds, 125 meters before the stop sign where it came to a stop.

There were no skid marks left by Car 2. The collision occurred at the stop sign, where Car 1 had stopped. After the collision, Car 2 came to a stop. Car 1's final velocity is unknown.

1. What was the potential energy of each car at the beginning of the problem.