試題詳解

39. Which of the following statements about gravity and planet motion is correct?
(A) In a non-uniform gravitational field, the center of gravity of an object is still located at the same position as its center of mass.
(B) The planet Mercury has smaller orbiting velocity than that of planet Jupiter
(C) On earth, the escape velocities of hydrogen and helium atouns are the same.
(D) If Newton's Law of gravity becomes F = Gm₁m₂/r^2.1, Kepler's second law (dA/dt = constant) is still correct.
(E) As Halley's Comet moves away from the sun, its velocity becomes greater and greater.