—What do you think of the equipment we’ve just bought? —You mean _____ over there? _____ is pretty good. A. the one; It B. that; That C. it; That D. that; It 答案:D在验证机械能守恒定律的实验中,打点计时器所用电源输出交流电压的频率为50Hz,下图为在实验中打点计时器打出的一条纸带,图中A点是重锤下落的起点,重锤的质量为m。从某一位置B开始,B、C、D、E各相邻计数点间的距离分别为s1、s2、s3,设打点计时器的打点周期为T,则打D点时重锤动能的表达式为____________。(2分)