平面简谐波的波动方程为y=0.01cos10π(25t-x)(SI),则在t=0.1

题型:单项选择题

问题:

平面简谐波的波动方程为y=0.01cos10π(25t-x)(SI),则在t=0.1s时刻,x=2m处质元的振动位移是:()

A.0.01cm

B.0.01m

C.-0.01m

D.0.01mm

考点:水利水电工程第二章普通物理第二章普通物理题库
题型:单项选择题

官渡之战是曹操统一北方的关键,在官渡之战中,曹操的对手是[ ]

A.周瑜

B.袁绍

C.刘备

D.孙权

题型:单项选择题

阅读理解

                                                      When milk arrived on the doorstep

     When I was a boy growing up in New Jersey in the 1960s, we had a milkman delivering milk to our

doorstep.His name was Mr.Basille.He wore a white cap and drove a white truck. As a 5yearold boy, I

couldn't take my eyes off the coin changer fixed to his belt.He noticed this one day during a delivery and

gave me a quarter out of his coin changer.

     Of course, he delivered more than milk. There was cheese, eggs and so on.If we needed to change

our order, my mother would pen a note- "Please add a bottle of buttermilk next delivery" -and place it in

the box along with the empty bottles.And then, the buttermilk would magically(魔术般)appear.

     All of this was about more than convenience. There existed a close relationship between families and

their milkmen. Mr. Basille even had a key to our house, for those times when it was so cold outside that

we put the box indoors, so that the milk wouldn't freeze. And I remember Mr. Basille from time to time

taking a break at our kitchen table, having a cup of tea and telling stories about his delivery.

     There is sadly  no home milk delivery today. Big companies allowed the production of cheaper milk,

thus making it difficult for milkmen to compete(竞争). Besides, milk is for sale everywhere, and it may

just not have been practical to have a delivery  service.

     Recently, an old milk box in the countryside I saw brought back my childhood memories. I took it

home and planted it on the back porch(门廊). Every so often my son's friends will ask what it is. So I

start telling stories of my boyhood, and of the milkman who brought us friendship along with his milk.

1. Mr. Basille gave the boy a quarter out of his coin changer ________.

A. to show his magical power

B. to pay for the delivery

C. to satisfy his curiosity

D. to please his mother

2. What can be inferred from the fact that the milkman had the key to the boy's house?

A. He wanted to have tea there.

B. He was a respectable person.

C. He was treated as a family member.

D. He was fully trusted by the family.

3. Why does home milk delivery no longer exist?

A. Nobody wants to be a milkman now.

B. It has been driven out of the market.

C. Its service is getting poor.

D. It is forbidden by law.

4. Why did the author bring back home an old milk box?

A. He missed the good old days.

B. He wanted to tell interesting stories.

C. He needed it for his milk bottles.

D. He planted flowers in it.

题型:单项选择题

CT值()。

A.是物体的X线衰减值

B.是一相对值

C.是物体的密度值

D.只反映了物体的厚度值

E.反映了X线管发出的X线强度

题型:单项选择题

眼球异物定位方法中定位最准确的是()

A.巴尔金氏定位法

B.角膜缘定位环法

C.吸盘式定位器法

D.薄骨位摄片法

E.无骨位摄片法

题型:单项选择题

造成钢筋长度和弯曲角度不符合图纸要求的原因是多方面的,主要有下料不准确,画线方法不对或误差大;用手工弯曲时,扳距选择不当等。

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