题目

某静电场中的电场线如图13-3-2所示，带电粒子在电场中仅受电场力作用，其运动轨迹如图中虚线所示，由M运动到N.以下说法正确的是（    ） A.粒子必定带正电荷B.粒子在M点的加速度大于它在N点的加速度C.粒子在M点的加速度小于它在N点的加速度D.粒子在M点的动能小于它在N点的动能图13-3-2 答案：解析：根据电荷运动轨迹弯曲的情况，可以确定点电荷受电场力的方向沿电场线方向，故此点电荷带正电，A选项正确.由于电场线越密，场强越大，点电荷受电场力就越大，根据牛顿第二定律可知其加速度也越大，故此点电荷在N点加速度大，C选项正确.粒子从M点到N点，电场力做正功，根据动能定理得此 第二节 书面表达（满分25分）   Teenagers杂志Conversation With Brad栏目的负责人Brad收到了李华的一封来信。仔细阅读下面的来信，帮助Brad用英语写一封回信, 给出分析并提出合理建议。? Dear Brad, ?     I’m a student from Xinhua Senior High School. I have some difficulty communicating with my parents. Although I have tried my best, I find it really difficult to make them satisfied……So I feel lonely sometimes. I would be grateful if you could give me some advice.?                                                                  Yours,                                                                          Li Hua 注意：1.可适当增加细节。?2．不少于100词。 Dear Li Hua, ?     I feel greatly honored to be trusted with your personal affairs. ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________