Posted by Paradise on .
b. Suppose that an object is 100 pounds when it is at sea level. Find the value of C that makes the equation true. (Sea level is 3,963 miles from the center of the earth.)
c. Use the value of C you found in the previous question to determine how much the object would weigh in:
i. Death Valley (282 feet below sea level)
ii. The top of Mt McKinley (20,320 feet above sea level)

Algebra (MAT 117) 
drwls,
What equation are you talking about and where does the C appear in it?
Weight is inversely proptional to mass and the square of the distance from the center of the Earth.
At the top of Mt McKinley, the elevation is 20,320 ft = 3.85 miles, which is 3966.85 miles from the center of the earth. The sea level weight gets multiplied by a factor
(3963/3966.85)^2 = 0.9981
A 100 lb object (at sea level) will weigh 99.81 lb atop Mt. McKinley. 
Algebra (MAT 117) 
Paradise,
original problem:
1.Many people know that the weight of an object varies on different planets, but did you know that the weight of an object on earth also varies according to the elevation of the object? In particular, the weight of an object follows this equation: where C is a constant and r is the distance that the object is from the center of the earth.
a. Solve the equation for r.
b. Suppose that an object is 100 pounds when it is at sea level. Find the value of C that makes the equation true. (Sea level is 3,963 miles from the center of the earth.)
c. Use the value of C you found in the previous question to determine how much the object would weigh in:
i. Death Valley (282 feet below sea level)
ii. The top of Mt McKinley (20,320 feet above sea level) 
Algebra (MAT 117) 
Anonymous,
Death Valley (282 feet below sea level)