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 909 lb.

Question

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

The answer will need to be in lbs.

Answer 1

We will use Universal Gravitation which follows an Inverse Square Law. This means if we double the distance, the force reduces to 1/2^2 = 1/4th of what is was.

a) 20,000 is 2 times 10,000 so we have 1/4th of 909 = 227 lbs

b) 30,000 is 3 times so we have 1/(3^2) = 1/9th of 909 = 101 lbs

c) 100,000 will be 1/100th of 909 = 9.09 lbs