EX 1. A driver slams on the brakes, leaving 88.0-m-long skid 8-1 marks on the level road. The coefficient of kinetic friction is estimated to be 0.480. How fast was the car moving when the driver hit the brakes? EX 2. An 18.0-kg suitcase falls from a hot-air balloon that is at 8-2 rest at a height of 385 m above the surface of Earth. The suitcase reaches a speed of 30.0 m/s just before it hits the ground. Calculate the change in internal energy of the system