问题 问答题

一列简谐横波沿x轴正方向传播,图1是波传播到x=5m的肘点时的波形图,图2是质点N(x=3m)从此时刻开始计时的振动图象,Q是位于x=10m处的质点,则:

(1)Q点开始振动时的振动方向如何?

(2)经过多长时间Q点第一次到达波峰?

答案

(1)图甲所示的波形为波刚传到M点的波形,由图甲可知,此时质点M的振动方向向下,故Q点开始振动的方向也向下.

(2)由图甲可以看出波长λ=4m,由图乙可以看出周期T=4s.

所以波速v=

λ
T
=
4
4
=1m/s.

由图甲还可以看出,最前面的波峰距Q点的距离△x=8m,故最前面的波峰传播到Q点,也就是Q点第一次出现波峰的时间.

则t=

△x
v
=
8
1
s=8s.

答:(1)Q点开始振动时的振动方向向下.

(2)经过8sQ点第一次到达波峰.

阅读理解

阅读理解

Saturday,March 20,2011

Dear Mom and Dad,

     The time has come:I'm graduating, and I thank you both for all your help during these

15 years. I still remember when you used to say, "You can be whatever you want" I'm so

glad you are my parents, especially when I hear kids say they don't get on well with theirs.

I'm glad that you support(支持) me when I decide to do anything. You always try to help,

and that's important to me .

     Dad, I remember when you first took me fishing. I loved going even though I never caught

anything. I also remember when you would get angry with me. I realize you were only trying

to show me the right way. When Iwould cry, you would always be there to try to cheer me

up. That's what I call a good, loving, caring dad. Sometimes you and Mom don't agree with

me, but you are there by my side in anything that I do, and that's why I love you both so much.

     Mom, I enjoy going out with you and having our happy time every Friday night, and I hope

that never changes. I love telling you everything;the best part about you is that you listen. I'm

glad we do a lot together. You love to have fun, and Dad does, too. You always give me your

opinion and I listen.

     Thank you for bringing me up.

                                                                                                        Love always,

1. Allison writes the letter to show __________ to her parents.

A. wishes

B. support

C. help

D. thanks

2. In Allison's opinion,other kids of her age may __________ their parents.

A. have problems with

B. get on well with

C. like to talk to

D. like to listen to

3. Father might get angry with her when Alilison __________.

A. didn't accept him

B. didn't do things in the right way

C. didn't catch any fish

D. didn't agree with her parents

4. The underlined part "and Dad does,too" in Paragraph 3 means "__________".

A. and Dad is funny, too

B. and so is Dad

C. and Dad has, too

D. and Dad also loves to have fun

5. What makes Allison and her mother good friends?

A. Cheering up each other.

B. Listening to each other and having fun together.

C. Encouraging each other.

D. Going out together.

判断题