The Setup:
We’re told that weight (gravitational force) is inversely proportional to the square of the distance from the center of the Earth. That means:
F = k / d^2
-where F is the force, k is the unknown constant of proportionality, and d is the distance
Or in plain English: as distance goes up, weight goes down, and it drops faster because of that square.
What we know:
- The astronaut weighs 215 lb on Earth’s surface.
- Radius of Earth = 4000 miles
- Astronaut is now 400 miles above the Earth → Total distance from center = 4400 miles
What we know but have to infer:
Weight is actually a measure of force in physics. Your weight is the force you have due to gravity pulling you toward the center of an object (in this case, the Earth).
Let's use the situation we have on Earth.
F = k / d^2
215 = k / (4000)^2
215 * (4000)^2 = k
k = 3,440,000,000
So, now that we know our constant, let's use it to find the weight 400 miles above Earth:
F = k / d^2
F = 3440000000 / (4400)^2
F = 177.69
Final Answer:
The astronaut will weigh about 177.69 pounds at 400 miles above Earth.
Still heavy enough to regret skipping leg day, but definitely lighter!
(Note: You may need to adjust for significant figures. The lowest significant figures in any of these numbers is 1, which would round our answer to approximately 180 pounds, but I have provided the decimal for added clarity.)
Jacob W.
10/12/25