2022英语周报七年级专项训练。答案

10.BC【解析】本题考查圆周运动,目的是考查学生的推理能力,小球在C点时,当管道对小球的作用力F向下时,由F mg=mR得速度v=3m/s,当管道对小球的作用力F向上时,由mg-F=mk得速度=1m/s,选项A错误;当F=22N时,由于F>mg,所以管道对小球的作用力F只能向下,由F mg=m得速度v=4m/s选项B正确;由几何关系可得斜面的长度L=2m,当小球在C点的速度为零时,小球从C点滑到斜面底端的时间最长,小球在斜面上由牛顿第二定律得a=gsin30°=5m/s2,由运动学知识可得L=1aF,所以最长时间为5s,选项C正确若小球从C点滑到斜面底端的时间为0.8s,由运动学知识可得L=a 1ar,得u=0.5m/,由mg-F=m需得F=.5N,选项D错误,

第三节书面表达wersionDear Sir or MadamMy name is Li Hua. As an exchange student fromChina, I am studying in a local school. I am reallydelighted to learn that a volunteer for your Chinese culturallic exhibition is required and I'm confident that I amtruly fit for thestart with, my advantage first lies in the fact that IChina and used to beand quite familiar with Chinese relics. Further-more, being an outgoing and optimistic boy, I am good atcommunicating with others and introducing Chinese cultureto the world is always my honor and my pleasure. Finallythere is no problem with my spoken English, as I havelived here for almost a year and I have no difficulty commu-dicating with others in EnglishI would really appreciate it if you can offer me thechance to be a volunteer in your museum. I am looking forward to your early reply.Li Hua

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