Darren L. answered 15d
ACT/SAT Math/English Prep Wizard | Yale Student | Perfect 800 on Math
Given:
Weight on Earth's Surface = 215 lbs
Radius of the Earth = 4000 miles
Height above the Earth's Surface = 400 miles
Because the problem tells us that the gravitational force is inversely proportional to the square of the distance, we can set up a general formula for this situation:
F = k / d2
Remember that F is also equal to the astronaut's weight, which is the measure of gravitational force as well. These values are equivalent and mean the same thing!
Here, k is our constant of variation, and d is the total distance from the astronaut to the center of the Earth. Before we do anything, we need to find k, which we can do by plugging in what we already know:
F = k / d2
215 = k / (4000)2
215 = k / 16,000,000
k = 3,440,000,000
And now we have our key formula to find the weight at 400 miles:
F = 3,440,000,000 / d2
But remember, our distance isn't just 400 miles, but rather the 400 miles on top of the radius of Earth (4000 miles).
So that makes our d = 400 + 4000 = 4400 miles
Now we just plug those values into the formula we found above:
F = 3,440,000,000 / d2
F = 3,440,000,000 / (4400)2
F = 3,440,000,000 / 19,360,000
F = 177.685
So the weight of the astronaut at 400 miles above Earth is approximately 178 pounds!
Jacob W.
10/12/25