题目

阅读下列短文, 按要求完成问题。Hi! Do you know the three children? They are in a happy family. Xiaoxue is beautiful. She is also a hardworking girl. She likes studying. She studies very well. She gets up early and finishes her breakfast quickly. Then she rides her bike to school. Liu Xing is a little lazy. He gets up late and then washes his face, brushes his teeth in a hurry. Then he goes to the bus stop without breakfast. He usually plays basketball after school. In the evening, he seldom does homework. He goes to bed late. Xiaoyu is a lovely boy. He gets up very slowly and then某宇航员登陆某颗星球后，想要测量该星球表面的重力加速度。为此该宇航员让一物体在重力作用下做平抛运动(空气阻力可以忽略)，并用携带的频闪照相机拍摄下了一段运动过程如图。已知频闪照相机的频率为f=10.0Hz，照片中的每个小方块都为正方形且代表的实际长度为L=2.50cm。(1)测量重力加速度的表达式应为g=___________；(用所给物理量的字母表达)(2)根据交待数据，可求得此平抛运动初速度为v0=____________，星球表面重力加速度g=_______________；(结果保留3位有效数字)(3)离开该星球时，宇航员让宇宙飞船在距离该星球表面非常近的圆轨道上飞行，并测出周期为T，假设该星球自转可以忽略，则该宇航员根据所测得的星球表面重力加速度g，以及已知的引力常量G，算出了该星球的质量M，则该宇航员计算的表达式为M=_____________。