题干

如图所示,清洗楼房光滑玻璃的工人常用一根绳索将自己悬在空中,工人及其装备的总重量为G。悬绳与竖直墙壁的夹角为α,悬绳对工人的拉力大小为F1,墙壁对工人的弹力大小为F2 , 则(   )
       

A:F1

B:F2Gtanα

C:若工人缓慢下移,增加悬绳的长度,则F1F2的合力变大来源:Z&xx&k.Com

D:若工人缓慢下移,增加悬绳的长度,则F1减小,F2增大

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答案(点此获取答案解析)

B

同类题3

阅读下面四篇短文,从各题所给的A、B、C、D四个选项中选出最佳选项。

    If you meet a British person in the street, it is very likely that he or she will apologize whether it is his or her fault (过错) or not.

    It seems that Britain is becoming a nation where everyone is saying sorry. Almost each person says sorry about eight times each day—and one in eight people apologize as many as 20 times a day.

    As you may have seen, the British apologize more often than members of other cultures. A research shows that in many cases, people's love of saying sorry in Britain goes a little further than it does for Americans. For example, about 15 British people would say ”sorry” while only 10 from the US would do this if they sneezed, if they corrected someone's mistake of if someone knocked into them.

    In the old days, “sorry” was used to express regret and sadness for having done something wrong. But now British people use the expression as a way of showing good manners. For example, they might say “sorry” instead of “excuse me”, “pardon”, “what” or “whatever”.

    People in Britain also use sorry when they share the same feeling with others—so they might say “sorry about the rain”.

    However, British people's use of “sorry” may make things very confusing (迷惑不清) and difficult for foreigners who are not familiar with their ways. But actually, people in Britain pay much attention to the feelings of others. This is the very reason why they apologize every day.