题目

在火车的车厢里用悬线吊着一个小球,由于在铁轨接合处的振动使球摆动.如果每根铁轨长12.5 m,吊小球的悬线长40 cm,那么当火车的速度达__________ m/s时,球摆动的振幅最大. 答案：10解析：摆球的固有周期T0=2π,驱动力的周期T′=,当T′=T0时,做受迫振动的摆球发生共振,振幅最大.=2π,v== m/s=10 m/s.   阅读理解  Tom Atkins saw an accident between two cars last month. He is a witness(证人) in court(法庭) today. You're going to hear the first lawyer(律师), then Tom , and then the second lawyer. 　　1st LAWYER :Mr. Atkins, would you please tell the court what you were doing when the accident happened and what you saw? 　　TOM: Yes. I was driving home from work. It was about fifteen past five, and there was a blue car in front of me. We were both driving along Harbour Road when a small White Ford suddenly shot out of a side road. It shot right in front of the blue car. The driver tried to stop, but it was impossible. He ran into the White Ford. 　　1st LAWYER: I see. Now, how fast was the ear in front of you going when the accident happened? 　　TOM：The blue ear? 30 miles an hour. Certainly no more than that. 　　1st LAWYER: And the White Ford shot without any warning? 　　TOM : No. 　　1st LAWYER :Thank you, Mr. Atkins. 　　2nd LAWYER: How can you be sure the blue car was doing 30? 　　TOM: Because I was doing 30, and the blue ear was not going any faster than I was. 　　2nd LAWYER :Are you sure of that, really? 　　TOM: Yes, I am. Really. 　　2nd LAWYER :Really? How can you he so sure, Mr. Atkins? Were you looking, at your speedometer(计速表) when the accident happened? 　　TOM: Of course not. I was looking at the road ahead. That was how I managed to the accident. 　　2nd LAWYER: Well, if you weren't looking at your speedometer, how can you possibly be sure how fast you were going? 　　TOM: Because I never go faster than 30 on that road. It's against the law. That's why. (1) Tom was driving ________. [　　] A. in front of the White Ford B. behind the blue car C. between the two ear D. after the two ears (2) The White Ford shot right_________. [　　] A. between Tom and the blue car B. behind the blue C. in front of the blue car D. in front of TOM (3) Tom was looking ________ when the accident happened. [　　] A. ahead B. at the speedometer C. at the blue carD. at the side way (4) When the accident happened Tom Atkins was driving [　　] A. 45B. 35C. 30D. 25 (5) The second lawyer is defending(辩护) [　　] A. the White Ford's driver B. the blue car's driver C. Tom D. nobody