Casey is driving a 1600 kg car toward the east. She goes through an intersection at a speed of 16 m/s (approximately 35 mph), the speed limit on both roads of the intersection. Kerry is driving a car of mass 1200 kg into the intersection, going north, and doesn't see or do not need a red light, and slams into Casey's car. The cars lock together and skid to a stop. Later, the two review the scene with the police. Skid marks from the instant after the collision reveal that the two cars were moving exactly northeast. Kerry claims to have been driving at the speed limit, but Casey says that Kerry seemed to be going over the speed limit before the collision.