2021-2022年英语周报高一外研第24期答案

25.解:(1)设粒子在磁场中运动的轨迹半径为R,则由几何关系:R √2Ra=d(1分)解得R=(√2-1)d(1分)由牛顿第二定律得qB=m设2(1分)设粒子在y轴上的坐标为(0,-y),则由动能定理qEy=-m(1分)解得=(3=22BE(1分)则S点坐标为(0.-3=2Bn2FE)(1分)(2)要使粒子由M点静止释放后均能沿垂直于斜边的方向射出磁场,则粒子在磁场中运动的半径R满足d=(2n 1)R(n=0,1,2…)(1分)由牛顿第二定律得qB=mR(1分)设粒子在y轴上的坐标为(0,-y),则由动能定理qEy=m2(1分)B-d-解得(2n 1)2mE(n=0,1,2…)(1分)故M点坐标为(0,-0BF2(2n 1)mE)(n=0,1,2…)(1分)(3)粒子在电场中的加速度为a,则qE=m(1分)粒子在电场中每单程的运动时间为,则y=at(1分)粒子在电场中总的运动时间t1=(2n 1)t(n=0,1,2…)(1分)解得-E(1分)粒子在磁场中做圆周运动的周期T=2(1分)粒子在磁场中总的运动时间a2= n(n=0,1,2…)(1分)解得t2=i maB(n=0,1,2…)(1分)运动的总时间t=t1 t22 n(n=0,1,2…)(2分)

第三部分写作第一节【写作指导】审题本题属于应用文写作中的邀请信立意写作时使用第一人称和第二人称,时态以一般将来时为主首段陈述写邮件的目的;中间段介绍讲座的写作时间、地点和内容,并说明邀请理由;最后思路几谋篇一段表达期待布局冂注意:考生也可以灵活安排每段的写作内容,但不可以遗漏要点推荐根据构思好的提纲确定写作可能用到的表达,表达to: invite, attend a lecture, waste food, raiseone' s awareness of等【佳作展台】Dear MikeI am writing to invite you to attend a lecture about Clear Your plateThe lecture is to be held in our school hall at 2: 30 pm nextThursday. It will be given by our headmaster, who will tell us the reasonsfor launching the campaign. Besides, he will talk about various activitiesto be carried out which are aimed at raising students awarenessof savingI think the lecture can help us have a better understanding of the campaignand form the habit of saving.i do hope you can join me. Please write back soonYours.Li hua亮点梳理】本文开篇点明写邮件的目的,接着详细介绍了此次讲座的相关情况,最后表达期望,内容完整,语勺流畅,同时使用了亮点词汇和句子。亮点词汇:atnd, launch, carry out, be aimed at, raIse one'sawareness of, have a better understanding of =o亮点句式:①非限制性定语从句 who will tell us the reasons forlaunching the campaign②强调句 i do hope you can join me

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