Newton's Law of Gravitation says that the magnitude of the force exerted by a body of mass on a body of mass is , where is the gravitational constant and is the distance between the bodies.

(a) Find . [What does the minus sign mean?]
(b) Suppose it is known that Earth attracts an object with a force that decreases at a rate of 2 N/km when km. How fast does this force change when km?