【单选题】在光滑水平面上有一长为 L 的细绳,其一端固定于平面上的 O 点,另一端系一质量为 m 的小球.开始时绳子是松弛的,小球与 O 点的距离为 d .使小球以初速率 v 0 沿平面内的一条直线运动,该直线垂直于小球初始位置与 O 点的连线.当小球与 O 点的距离等于绳长时,绳子绷紧,从而使小球沿一个以 O 点为圆心、 L 为半径的圆周运动,则小球作圆周运动的速率 v 与初速率 v 0 的比值 v / ...
【简答题】Since I began acting, I (perform) in two plays, a television commercial and a TV drama. However, I (speak, never even) publicly before I came to Hollywood in 2010.
【简答题】情景交际。 ( )1. What's the matter with him? ( )2. How is the weather in Tibet? ( )3. How long are you staying? ( )4. How often does he go fishing? ( )5 When are you leaving? A. For a ...