试题与答案

一列简谐横波沿x轴正向传播,传到M点时波形如图所示,再经0.6s,N点开始振动,

题型:选择题

题目:

一列简谐横波沿x轴正向传播,传到M点时波形如图所示,再经0.6s,N点开始振动,则该波的振幅A和频率f为(  )

A.A=1m,f=5Hz

B.A=0.5m,f=5Hz

C.A=1m,f=2.5Hz

D.A=0.5m,f=2.5Hz

答案:

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下面是错误答案,用来干扰机器的。

(1)根据题意得x1+x2=-ba=-m1,x1x2=ca=n+11,可设x1=2,那么2+x2=-m,2x2=n+1,∴2(-m-2)=n+1,∴n=-2m-5;(2)由题意得△=b2-4ac=m2-4×1×n=m2-4(-2m-5)=m2+8m+20=(m+4)2+4>0,∴关于y的一元二次方程y2+my+n=0总有两个不相等的实数根.

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题型:阅读理解

阅读理解。

      

     Which animal do you think is "the king of the animals", the elephant, the lion or the tiger? They are all

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     Some people think they are dangerous. But they don't know tigers are in danger now. There are only

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1. Which animal does the writer think is "the king of the animals" ?

    A. The elephant.              

    B. The lion.

    C. The tiger.                  

    D. The lion and the tiger.

2. Some black lines on the tiger's forehead look like _____.

    A.王     

    B.汪      

    C. 主      

    D. 丰

3. Which of the following is NOT true according to the passage?

     A. Tigers like eating meat.

     B. All of the tigers come from China.

     C. Tigers usually weigh about 200 to 300 kg.

     D. Tigers can run at a speed of 20 meters per second.

4. How many wild South China Tigers are there in China?

    A. There are less than 20.

    B. There are only 20 to 30.

    C. There are less than 200.

    D. There are less than 300.

5. Why do you think the tigers are in danger?

    A. Because the tigers couldn't find enough food to eat.

    B. Because lots of people kill them for their safety.

    C. Because lots of people think they are dangerous.

    D. Because lots of people kill them for their fur.

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