题目

The upset mother thought to herself, “If only I ______ what's going on in my little boy's head right now.” A . know B . knew C . have known D . had known 答案：B1．在一个半径为R的星球表面，离地h处无初速释放一小球，不计阻力，小球落地时速度为v．已知引力常量G，求：（1）这颗星球表面的重力加速度；（2）这颗星球的质量；（3）若星球的自转周期为T，求这颗星球同步卫星的高度．