Two roads meet perpendicularly at an intersection. A truck is driving south towards the intersection at 20 meters per second. A car has already passed througth the intersection, and is driving east away from the intersection at 10 meters per second. At the instant when the truck is 30 meters from the intersection and the car is 40 meters past the intersection, find the rate of change of the distance between the two vehicles. Are they getting further apart or closer together?