試題詳解

46. Inside a planet, the mass density is usually not homogeneous across the planet. However, if a spherical planet is decomposed into concentric spherical shells, the mass density is approximately the same for each concentric shell. As a result, for a spherical planet X of radius R, the mass density can be treated as a function of its distance to the center of the planet,. Assuming the gravitational field strength at the surface of the planet is g₀, which of the following statements is true?

(A)At r = R/2, the gravitational field strength is still g₀.
(B)At r = R/2, the gravitational field strength is equal to 0.
(C)At, r = R/2 the gravitational field strength is equal to g₀/2.
(D)At r = R/2, the gravitational field strength is smaller than g₀/2 but not equal to 0.
(E)At r = R/2, the gravitational field strength is greater than g₀/2 but not equal to g₀.