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

(a) Find [math]. [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 [math] km. How fast does this force change when [math] km?

(a) [math]
(b) N/km