题目

从地面以大小为v1的初速度竖直向上抛出一个皮球,经过时间t皮球落回地面,落地时皮球的速度大小为v2.已知皮球在运动过程中受到空气阻力的大小与速度的大小成正比,重力加速度大小为g.下面给出时间t的四个表达式中只有一个是合理的.你可能不会求解t,但是你可以通过一定的物理分析,对下列表达式的合理性做出判断.根据你的判断,你认为t的合理表达式应为(重力加速度为g) ( )A. B. C. D.完成对话，每空一词。John: Tim, glad to see you again. ______ (1) you enjoy your summer holiday? Tim: Yes, how about you? Did you stay at home?John: ______(2). I went to Emei Mountain in Sichuan and had a wonderful time there. Tim: Really? So did I.John: And I ______(3) to the top of the mountain. Tim: So ______ (4)I.John: And I stayed there for a night, and the next morning I saw the sunrise. It was great! Tim: Oh, dear!______ (5)______ (6)I.John: ______ (7) didn't I see you there?Tim: I went in late July. And you? John: Early August.What a ______ (8) we didn't go there at the same time!