Suppose that two straight roads intersect in a right angle. A car travels north on the north-south road at 50 mph. A truck travels east on the east-west road at 70 mph. How fast is the straight line distance between the car and the truck changing at a moment when the car is 30 miles south of the intersection point and the truck is 40 miles east of the intersection point? Are the automobiles getting farther apart or closer together at this moment in time and why?

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