試題詳解

25.A planet has mass one-half the mass of the earth. What radius must it have so that the acceleration due to gravity at its surface is the same as the acceleration due to gravity at the surface of the earth? (Answers are expressed in terms of the radius of the earth.)
(A) R = 1.41 R_E
(B) R = 0.71 R_E
(C) R = 2.00 R_E 
(D) R = 0.50 R_E