初一2019~2022学年英语周报第47期答案

15.解:(1)设电场的方向与y轴正方向的夹角为0,如图所示。根据题意,有正ing1(2分)cst(2分)解得s=mB(1分)=1/qE产(1分)即电场方向与y轴正方向夹角的正弦值sin=m,(1分)(2)OP=ovr=ot2E2r22(3分)即P点的坐标为(0,-、厘EF-82),(1分(3)如图所示微粒第一次过x轴P1点进入第一象限,速度大小v,OP1=at,微粒进入第一象限做匀速圆周运动,则圆周运动的半径R√GEP=mBq,P1P2=2R(1分)微粒从P2点回到第四象限,经电场后再回到P1点。根据运动的对称性微粒从P2点到P1点需要的时间为2t,在水平方向,微粒做初速度为零的匀加速运动,方向向左,到达P1点的水平速度为2(2分)水平方向,有P1P2=2R=2bt(2分)=vt(1分)解得一{√g…,(分)

第二节:书面表达〈满分25分NoticeAimed at arousing us students'awareness of obeying traffic rules, a social practice, organized by ourschool, will be held next week, whose theme is"Obey the traffic rules, do as a civilized student.There are some arrangements as follows. Every class divided into three groups should arrive at thecrossroads assigned at 7 am, after which Group one set about hanging the traffic slogans, while Group twowill help the police clear the traffic. The rest will distribute the hand-made brochures concerning trafficregulations to passers-by, reminding them of being civilized residentsEveryone is expected to be punctual and takes an active part in itthe Students' ui

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