题目

如图4-3-17所示，汽车在倾斜的弯道上拐弯，弯道的倾角为θ，半径为r，则汽车完全不靠摩擦力转弯的速率是________________. 图4-3-17 答案：解析：汽车靠地面支持力沿水平方向的分力提供向心力，有mgtanθ=m，所以v=.答案： 请认真阅读下列短文，并根据所读内容在文后表格的空格处填入最恰当的单词。注意：每个空格填1个单词。 　　No one can avoid being influenced by advertisements．Much as we may pride ourselves on our good taste, we are no longer free to choose the things we want, for advertising exerts(施加)some influence on us．In their efforts to persuade us to buy this or that product, advertisers have made a close study of human nature and have classified(分类)all our little weaknesses． 　　Advertisers discovered years ago that all of us love to get something for nothing．An advertisement which begins with the magic work FREE can rarely go wrong．These days, advertisers not only offer free samples, but free cars, free houses, and free trips round the world as well．They design hundreds of competitions which will enable us to win huge sums of money．Radio and television have made it possible for advertisers to draw the attention of millions of people in this way． 　　During a radio program, a company of biscuit manufacturers once asked listeners to bake biscuits and send them to their factory．They offered to pay ＄10 a pound for the biggest biscuit baked by a listener．The response to this competition was active．Before long, biscuits of all shapes and sizes began arriving at the factory．One lady brought in a biscuit on a wheelbarrow．It weighed nearly 500 pounds．All the biscuits that were sent were carefully weighed．The largest was 713 pounds．It seemed certain that this would win the prize．But just before the competition closed, a lorry arrived at the factory with a truly large biscuit which weighed 2,400 pounds．It had been baked by a college student who had used over 1,000 pounds of flour, 800 pounds of sugar, 200 pounds of fat, and 400 pounds of various other ingredients．The factory had to pay more money than they had expected, for they bought the biscuit from the student for ＄24,000．