题目

如图所示，质量为60g的铜棒长为a=20cm，棒的两端与长为L=30cm的细软铜线相连，吊在磁感应强度B=0.5T、方向竖直向上的匀强磁场中.当棒中通过恒定电流I后，铜棒向上摆动，最大偏角θ=60°，g取10m／s2，求: (1)铜棒中电流I的大小. (2)铜棒在摆动过程中的最大速率(结果保留一位有效数字) 答案：(1)    (2)1m/sHow often do you change your hairstyle or ask for new dresses? You may try to follow trends in Western countries，but your peers(同龄人)in the United States don't care as much about fashion(时尚)as you do． A recent survey among high school students in China，Japan，South Korea and the US found that Asian teenagers care more about their looks than young people in the US． This survey was held in 156 high schools in the four countries. More than 7,000 teenagers were questioned about their view on life and the world. South Koreans, at 83 percent, cared most about their appearance. They were followed by the Chinese and Japanese while US students showed the least interest in fashion at only 33 percent.“The different results show differences of cultural background,” said Sun Yunxiao from the China Youth and Children Research Centre.He explained that in the US there are many different standards of beauty, so teens are more likely to be confident about their appearance.US teenagers’ high self-confidence is showed in survey. About 85 percent are happy with themselves. The percentage of self-confident Chinese students stands at only 30 percent. Strong ambition( 雄心) is seen in Chinese high schools. Only two in five high school students are satisfied with “an average living”. Koreans are next at 48 percent，Japanese come in at 66 percent and Americans are at 71． “According to the survey，Chinese students are happy. But Chinese students need to be more independent and learn how to relax．”said Sun．小题1:According to the survey，_________ cared little about their appearance．A．the Chinese teenagersB．the American teenagers．C．the Korean teenagersD．the Japanese teenagers小题2:Sun Yunxiao’s words means ___________.A．the different standards of beauty cause the different attitudes toward fashionB．the Chinese teens should have a stronger desire to make a difference．C．the Chinese students are satisfied with the society mostD．the Chinese students agree that they should follow their own interests rather than those of others小题3:The underlined word “standards’’ in the sixth paragraph means __________.A．rulesB．backgroundsC．valuesD．interests小题4:From the 8th paragraph we may 1earn that __________．A．Asian teenagers care more about their looks than young people in the US B．US students showed the most individuality(个性)among the four countriesC．Chinese students need to be more independent and learn how to relaxD．American students have the least ambition among the four countries小题5:What does the passage mainly talk about?A．A survey about the attitudes towards the fashion．B．How Asian teenagers care more about their looks than young people in the US．C．Why Chinese students are happy．D．Why Chinese students should be more independent and learn how to relax