如下图所示，一列简谐横波在x轴上传播，图甲和图乙分别为x轴上a_爱下问搜题

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问题选择题

如下图所示，一列简谐横波在x轴上传播，图甲和图乙分别为x轴上a、b两质点的振动图象，且 =" 6" m．下列判断正确的是

A．波一定沿x轴正方向传播

B．波长一定是8 m

C．波速可能是2 m/s

D．波速一定是6 m/s

答案

答案：C

分析：根据两振动图象读出a、b两质点在同一时刻的状态，结合波形，分析a、b间距离x_ab与波长的关系，得到波长的通项，求出波速的通项，再求波速的特殊值．

解答：解：

A、由振动图象无法比较a、b两质点振动的先后，所以无法判断波的传播方向．故A错误．

B、若波沿x轴正方向传播时，由振动图象读出t=0时刻，a质点经过平衡位置向下运动，而b位于波峰，结合波形得到：

x_ab=（n+1/4）λ，n=0，1，2…得到波长为λ=4x_ab/(4n+1)= 24/(4n+1)m，波速为v="λ/" T=6/(4n+1)m/s

同理可知，若波沿x轴负方向传播时，波长为λ=24/(4n+3)m，波速为

v="λ/" T=6/(4n+3)m/s

由于n是整数，λ不可能等于6m．故B错误．

C、由波速为v="λ/" T=6/(4n+3)m/s得，当n=0时，v=2m/s．故C正确．

D、由上可知，波速不一定等于6m/s．故D错误．

故选C

点评：本题通过两个质点的振动图象，读出同一时刻两质点的状态，根据波形，得出两点间距离与波长的关系，是典型的多解问题．

单项选择题

男性，45岁，腰痛多年，时轻时重，伴双下肢后外侧痛。10天前搬重物后腰腿痛加剧，并出现麻木与排尿困难。查体：腰运动受限，椎旁压痛向下肢放散，直腿抬高试验与加强试验阳性。鞍区痛觉减退。

最主要的治疗措施是

A．卧硬床休息

B．牵引

C．硬脊膜外腔强的松龙注射

D．手术

E．激素和非甾体类抗炎剂

完形填空

I was late for the school bus and rushing to get ready. My dog, Tippy, got to the front door and lay down in front of it – his way of asking to be petted. I______his begging for affection (喜爱), and ran for the waiting bus.
______, that afternoon, when I came home, Mom said to me______, “Honey, I have some______news that I need to tell you. This morning, while you were at school, Tippy was hit by a car and______. I’m so sorry.”
“No! It’s not true!” I was______. I couldn’t believe her. “Tippy, come here! Come on, boy!” I called and called for him. I waited. He didn’t come. Feeling______, I wandered into the living room. I didn’t cry that night. I still couldn’t believe that he was______.
When I got off the bus the next day, the silence at home was deafening. , my sobs (哭泣) erupted (喷发) like lava (熔岩) from a volcano. I couldn’t stop______. I hadn’t even petted him when I left.______could I have known that was my last chance? I cried until I felt empty inside.
Time passed, and against my will, I started to______some things. I realized what little control any of us have over what happens ______ a dog. We can do everything right, but______things can still happen. But good things can happen too. That’s______. The best way to deal with the hard times is to understand what you and get them through when they come, and to remember that hard times always______.
I now deeply understand the “circle of life”. Everyone is born, everyone______, and that’s the way it is. If dogs never died, there would be no______for others like Belle – my new dog.
Best of all, I realized that Tippy______all of my old memories of him. And they come to me every time I call!

A．in disagreement	B．in anger
C．in silence	D．in shock

A．came through	B．went through
C．looked through	D．watch through

C．possibility

C．left behind