Question

A space probe is launched from Earth headed for deep space. At a distance of 10,000 miles from Earth's center, the gravitational force on it is 600lb. What is the size of the force when it is at each of the following distances from Earth's center?
A] 20,000 miles
B] 30,000 miles
C] 100,000 miles

Answer 1

The force is proportional to the inverse of the square of the distance from the center of Earth.

Answer 2

so in case A), the distance is twice as far as the reference distance of 10,000 miles.
As force is proportional to 1 / {distance squared}, the force will be 1 / 2^2 (i.e. 1/4) of the force at the reference distance (i.e. 1/4 * 600 = 150 lb).