【单选题】如图所示,一个质量为 m 、电荷量为 q 的带电小球从 M 点自由下落。 M 点距场区边界 PQ 高为 h ,边界 PQ 下方有方向竖直向下、电场强度为 E 的匀强电场,同时还有垂直于纸面的匀强磁场。小球从边界上的 a 点进入复合场后,恰能做匀速圆周运动,并从边界上的 b 点穿出。重力加速度为 g ,不计空气阻力,则下列说法中正确的是 ( ) 。
C.
小球从 a 运动到 b 的过程中,小球和地球系统机械能守恒
【简答题】Americans have many expressions ___(used, using) the word “dogs”. Nowadays people in the United States love their dogs and ______(threat, treat)them well. They take their dogs ____(for , on ) walks,l...
【简答题】Among the college students nowadays, there is a tendency to attach too much importance to foreign holidays, while they neglect our owns without an understanding about the meanings of our traditional f...
【判断题】毛石基础宜用于地下水位高,地震频发的地区。
【判断题】毛石基础宜用于地下水位高,地震频发的地区。
【判断题】重力的方向垂直地面向下,重力加速度是9.8m/
【简答题】l Dog talk: Every dog has its day Americans have many expressions using the word “dog.” Nowadays people in the United States love their dog and treat them well. They take their dogs for walks, let the...