posted by Josh .
Newton's Law of Gravitation says that the magnitude F of the force exerted by a body of mass m on a body of mass M is the following.
Here G is the gravitational constant and r is the distance between the bodies.
(a) Find dF/dr
(b) Suppose it is known that Earth attracts an object with a force that decreases at the rate of 2 N/km when r = 30,000 km. How fast does this force change when r = 15,000 km?