【单选题】(1- 质点系角动量) 质量 m=20 g 的子弹,以初始速度 v 0 =400 m/s 的速率沿图示方向(与竖直方向成 30 °角)射入一原来静止的质量 M=980 g 的摆球中心,摆线长度不可伸缩,摆线最高点到摆球中心的距离 l =1.0m ,摆球和子弹一起运动时在最低点的共同速度大小为()( g 取 10m/s 2 )
【简答题】听对话,回答问题。 1. Why did David NOT go home for the holidays? A. Because he did not want to see his family. B. Because he was too busy with his studies to go home. C. Because the snow stopped the trains fr...