题目

如图所示，A、B两物体相距x＝7 m，物体A以vA＝4 m/s的速度向右匀速运动，而物体B此时的速度vB＝10 m/s，只在摩擦力作用下向右做匀减速运动，加速度a＝－2 m/s2。那么物体A追上物体B所用的时间为( )A. 10 s B. 9 s C. 8 s D. 7 s 答案：【答案】C【解析】本题是匀速追匀减速，先判断B物体停止时A物体有没有追上B物体；然后再据追上时两物体的位移关系列式求出物体A追上物体B所用的时间。设物体B速度减为零的时间为，则；在5s内，物体B的位移，物体A的位移，由于，5s内物体A未追上物体B。5s后，物体B静止不动，设物体A还需时间追上About five years ago I began to study at a new school, when my family moved to Iowa. I was just a little    1  ,wondering whether I could get on well with my classmates.Lucy, a girl in my    2  , who I thought wasn’t ready to accept a  3   girl, didn’t like me from the start.    4  ,I was pretty sure she hated me. When I asked her a question, I could __5__ she thought I was a total fool.My teacher made us   6   next to each other for the last term. Lucy was not happy. However, I kept   7   at her, though she rolled her eyes, and I kept telling her that she was beautiful.Finally, Lucy let me   8   to her, even when her friends were around. She ___9___ telling me how beautiful I looked. I still remember the ___10___ time when she smiled at me and said that, and I smiled right back, saying    11  to her. One day Lucy invited me over to her house, and talked to me all the time   12   her other friends. That day Lucy , the girl who had hated me, called me her best deskmate. After that, we   13   friends for years.I moved to Arizona later, but I will never   14   Lucy. I still remember she considered me her   15  at first. During that time it felt like I was    16  my time, and losing my dignity(尊严)，but I still smiled at Lucy even when she    17  me. I’m not stupid; I didn’t think she was   18   in doing those things, but I still put up with it. And finally we became great friends.Not long ago, I read the   19   of Abraham Lincoln, “Am I not destroying my enemies when I make friends of them?” I smiled, thinking of Lucy. It just   20   me how great a friend I used to have.【小题1】A．sadB．surprisedC．worriedD．eager【小题2】A．schoolB．classC．teamD．city【小题3】A．positiveB．successfulC．newD．common【小题4】A．UsuallyB．ActuallyC．FinallyD．Fortunately【小题5】A．describeB．proveC．tellD．accept【小题6】A．sitB．speakC．standD．live【小题7】A．shoutingB．laughingC．pointingD．smiling【小题8】A．writeB．replyC．talkD．listen【小题9】A．startedB．mindedC．consideredD．avoided【小题10】A．rareB．nextC．lastD．first【小题11】A．helloB．thanksC．sorryD．bye【小题12】A．according toB．thanks toC．except forD．instead of【小题13】A．servedB．appearedC．seemedD．stayed【小题14】A．forgetB．leaveC．missD．teach【小题15】A．enemyB．heroC．friendD．leader【小题16】A．changingB．managingC．wastingD．enjoying【小题17】A．took care of B．took the place ofC．made fun ofD．get away from【小题18】A．rightB．proudC．interestedD．busy【小题19】A．booksB．wordsC．storiesD．experiences【小题20】A．taughtB．advisedC．warnedD．reminded