七年级新目标英语周报第30期2021-2022答案

书面表达One possible version:NOTICEA sports meeting will be held in the playground of our school from next Thursday to FridayAs you know, the pressure of study is very heavy now, especially for those senior 3. So the purpose of the sports meeting is to letevery student get relaxed, as a result of which we students can live happily and heal thilyEveryone is welcome to take part in it. Those who perform excellently at the sports meeting will get prizes. But don' t take theresults so serously because taking part is more important than the result. Good luck to everyone!

8.C【解析】0~4时间内,力传感器示数为0,说明水平面对物体B的静摩擦力没有达到最大值,~时间内力传感器的示数逐渐增大,说明水平面对物体B的静摩擦力已达到最大值物体B对物体A有向右的静摩擦力,a时刻后力传感器的示数不变,说明物体B相对物体A向右运动物体A受到滑动摩擦力,则e时刻A、B两个物体间的静摩擦力达到最大值,fmx=k(-h1),A项错误;由于物体B运动后物体A静止不动,则A、B两个物体间有滑动摩擦力,等于k(43-41),而水平向右的拉力大小为k2,因此水平面与物体B之间的滑动摩擦力为k2,C项正确项误;由于各接触面上压力大小来知,故不能求出摩擦因数,D项错误

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