题目

如图所示，在竖直向下的匀强电场中有一带负电的小球，自绝缘的斜面A点由静止开始滑下，接着通过半径为R绝缘的离心轨道最高点B。已知小球的质量为m，带电量为q，匀强电场的场强为E，且mg>qE，运动中摩擦阻力及空气阻力不计，则h至少应为多少？当h取最小值时，小球对最低点的压力为多少？ 答案：Why won’t the woman go to the concert (音乐会)?A. Because she hasn’t got a ticket for the concert.B. Because she is too busy at work.C. Because of some visitors’ arrival. C 【解析】M: Mary, I have an extra ticket for the concert tonight. Can you come with us? W: I’d love to, but we’ll have some visitors tonight. Thank you, anyway. 听力题，解析略。