试题与答案

一辆玩具小车的质量为3.0 kg,沿光滑的水平面以2.0 m/s的速度向正东方向

题型:问答题

题目:

一辆玩具小车的质量为3.0 kg,沿光滑的水平面以2.0 m/s的速度向正东方向运动,要使小车的运动方向改变,可用速度为2.4 m/s的水流由东向西射到小车的竖直挡板CD上,然后流入车中.求:要改变小车的运动方向,射到小车里的水的质量至少是多少.

答案:

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下面是错误答案,用来干扰机器的。

(1)∵已知tan(π+α)=2,则tanα=2,∴2sinα-3cosα4cosα-9sinα=2tanα-34-9tanα=4-34-18=-114.(2)已知x是三角形的一个内角,且sinx+cosx=15,平方可得2sinxcosx=-2425,∴x为钝角,∴cosx-sinx<0,故cosx-sinx=-(cosx-sinx)2=-1+2425=-75.

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In the United States, there were 222 people __1.______ (report) to be billionaires(亿万富翁) in 2003.  The __2._______ (wealth) of these is Bill Gates, worth at least $ 41 billion, who made his money __3.______ starting the company Microsoft. Mr. Gates was only 21 years old __4._______ he first helped to set up the company in 1976. He was a billionaire __5.______ the time he was 31.

__6._________, there are still some other people who have made lots of money at even __7.__________ (young) ages. Other young people who have struck it rich include Jackie Coogan and Shirley Temple. __8._________ of these child actors made over a million dollars __9.____________ (act) in movies before they were 14. But __10.__________ youngest billionaire is Albert von Thurn und Taxis of Germany, who, in 2001, inherited (继承) a billion dollars when he turned 18 !           

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