英语周报高一北师大12期2021-2022答案

18.【关键能力】本题考查考生的分析综合能力,需应用电磁感应、牛顿第二定律、动量定理等知识解题【解题思路】(1)a棒在倾斜导轨上匀速运动时,有mosin 6=BⅣ(1分)1民s1分)a、b两棒材料和横截面积均相同,a棒的长度是b棒的2倍,则b棒的电阻为2,质量为,a棒为等效电源内阻为R定值电阻与b棒并联,RR+长并R(1分)解得4 meRsinθ3B2(2分)(2)a棒进入水平导轨后,感应开关断开,a棒在安培力的作用下做减速运动,b棒在安培力的作用下做加速运动,当两棒速度相等时距离最小,设相同速度为n1,a、b两棒的位移分别为x和x,安培力对a、b两棒的冲量大小分别为l、l,根据/=Ft=BL可知l=2/(l分)对a棒有-1=m1-m(1分)对b棒有1=2"(1分)解得n12 meRsin e(1分(3)a、b两棒在水平导轨上运动过程中,设△内流过b棒的电流大小为i,由于Δt极小,可视为定值,对b棒有2×△又i=△q则2B△y=12m△(1分)可得∑Bl△q=∑分)解得Bl=m1其中g=itB△S(1分两棒串联则Ra2=2(1分)(1分)解得x-2=mE8m(1分)临考锦囊》多过程运动问题可按照先后顺序将运动分解为多个小过程运动。本题中有两个过程,一是金属棒在倾斜导轨土向下运动,是单棒切割磁感线模型,平衡时重力澄倾斜导轨向下的分力与安培力大小相等,注意电路的连接关系;二是两金属棒在水平导轨上运动,b棒加速,a棒减速,当两棒速度相等时距离最近在此过程中两棒所受安培力不相等,系统动量不守恒,需要应用动量定理解题。

读后续写Possible version lI stared at the paper and then looked around. I was cold. Although I could not see my sistersnor the new house, which was hidden from my sight by a grey wall, I got the feeling that I was notalone. Walking along the shore was a tall familiar figure who looked lost in his thoughts. I lookedgain at the paper in my hand, closed my eyes and wishedAs /opened my eyes, I found my father was standing right beside me. Happy birthday, sonhe said, patting my shoulder gently. I smiled up at him and took his hand. Looking back, life fromthat day on marked the start of a close bond and a strong friendship with my father. What was mybirthday surprise? Wishes do come truePossible version 2I stared at the paper and then looked around. On the backside, there was a map. I noticed thatit was clearly leading me in a direction, but who could have sent this? I stood there in silence andstudied it. I decided to follow the map and it led me down the beach until I reached a staircase. Iooked back and could no longer see my siblings. I continued to follow the point on the map, untilI unexpectedly lost my footing and fell zksq down the stepsAs I opened my eyes, I found my father was standing right beside me. Happy birthday, sonhe said, patting my shoulder gently. Then he asked how I had come upon this place? I explained tohim that I had found the bottle in the ocean and when I opened it had the words on it. Shocked bythe message, my father realized what I had found I threw this bottle into the ocean many years agowhen I was alone. he said. I used to come to this exact place to get away from everyone else. NowI get to share this experience with you. What a birthday surprise

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