Questions 4-5
The magnitude of the Earth’s gravitational force on a point mass is F(r), where r is the distance from the Earth’s center to the point mass. Assume the Earth is a homogeneous sphere of radius R.
Suppose there is a very small shaft in the Earth such that the point mass can be placed at a radius of R/2. What is
A. 8
B. 4
C. 2
D. 1/2
E. 1/4
(GR9277 #05)
Solution:
Newton's law of gravity becomes a linear law inside a body → F ∝ r
F(R) ∝ R
F(R/2) ∝ R/2
Answer: C
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