题目

一列简谐横波沿x轴负方向传播，波速v=4 m/s，已知坐标原点（x=0）处质点的振动图象如图a所示，在下列4幅图中能够正确表示t=0.15s时波形的图是  答案：A解析:由，机械波在0.15s间向左传播距离为0.6m，T=0.4s，0.15s质点经历四分之一个周期不到半个周期，在t=0时刻原点的质点向上振动，经历0.15s时应越过最高点，向下运动，没有运动到平衡位置，由此判断A对 The play had already been on for quite some time when we _____ at the New Theatre. [     ]A. have arrived B. arrived C. had arrived D. arrive