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问题 填空题

一辆以12m/s的速度在水平路面上行驶的汽车，在刹车过程中以3m/s2的加速度做匀减速运动，那么t＝5s时物体的位移是_________m。停车前最后1秒内物体的位移是_________m。

答案

24   m、    1.5  m  

分析：先求出汽车刹车到停止所需的时间，因为汽车停止后不再运动，然后根据x=v0t+at2/2，求出汽车的位移．

解答：解：汽车刹车到停止所需的时间t0==s=4s＜5s

所以5s内的位移等于4s内的位移．

x=v0t+at2/2=12×4-3×16m/2=24m

最后1s内物体的位移为s= at2/2=3×12/2m=1.5m

故答案为：24，1.5m

点评：解决本题的关键知道汽车刹车停止后不再运动，以及掌握匀变速直线运动的位移时间公式x=v0t+at2/2

单项选择题

Advertisers tend to think big and perhaps this is why they’re always coming in for criticism. Their critics seem to resent them because they have a flair for self promotion and because they have so much money to throw around. "It’s iniquitous," they say, "that this entirely unproductive industry (if we can call it that) should absorb millions of pounds each year. It only goes to show how much profit the big companies are making. Why don’t they stop advertising and reduce the price of their goods After all, it’s the consumer who pays... "
The poor old consumer! He’d have to pay a great deal more if advertising didn’t create mass markets for products. It is precisely because of the heavy advertising that consumer goods are so cheap. But we get the wrong idea if we think the only purpose of advertising is to sell goods. Another equally important function is to inform. A great deal of the knowledge we have about household goods derives largely from the advertisements we read. Advertisements introduce us to new products or remind us of the existence of the ones we already know about. Supposing you wanted to buy a washing machine, it is more than likely you would obtain details regarding performance, price, etc. , from an advertisement.
Lots of people pretend that they never read advertisements, but this claim may be seriously doubted. It is hardly possible not to read advertisements these days. And what fun they often are, too! Just think what a railway station or a newspaper would be like without advertisements. Would you enjoy gazing at a blank wall or reading railway bylaws while waiting for a train Would you like to read only closely printed columns of news in your daily paper A cheerful, witty advertisement makes such a difference to a drab wall or a newspaper full of the daily ration of calamities.
We must not forget, either, that advertising makes a positive contribution to our pockets. Newspapers, commercial radio and television companies could not subsist without this source of revenue. The fact that we pay so little for our daily paper, or can enjoy so many broadcast programs is due entirely to the money spent by advertisers. Just think what a newspaper would cost if we had to pay its full price !
Another thing we mustn’t forget is the "small ads" which are in virtually every newspaper and magazine. What a tremendously useful service they perform for the community! Just about anything can be accomplished through these columns. For instance, you can find a job, buy or sell a house, announce a birth, marriage or death in what used to be called the "hatch, match and dispatch" column but by far the most fascinating section is the personal or "agony" column. No other item in a newspaper provides such entertaining reading or offers such a deep insight into human nature. It’s the best advertisement for advertising there is!

Why do the critics criticize advertisers

A．Because advertisers often brag.
B．Because critics think advertisement is a "waste of money".
C．Because customers are encouraged to buy more than necessary.
D．Because customers pay more.
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单项选择题 案例分析题

关闭门窗，点燃一盘蚊香，使蚊香的烟垂直向上（不受室外气流的影响）。在蚊香的等距离左右两侧分别放一只1000W的电炉、一面盆冰块。

此实验可模拟（）

A.季风的形成

B.锋面的活动

C.台风的形成

D.寒潮的形成
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