问题 单项选择题

如图所示,弹簧秤、绳和滑轮的重力不计,摩擦力不计,物体重量都是G.在甲、乙、丙三种情况下,弹簧的读数分别是F1、F2、F3,则()

A.F3>F1=F2

B.F3=F1>F2

C.F1=F2=F3

D.F1>F2=F3

答案

参考答案:B

解析:

甲图:物体静止,弹簧的拉力F1=mg;

乙图:对物体为研究对象,作出力图如图。

由平衡条件得

丙图:以动滑轮为研究对象,受力如图.由几何知识得F3=mg.故F3=F1>F2

阅读理解

阅读理解。

     When the earthquake hit Japan on March 11,workers in a supermarket in Japan didn't run away when

they felt the shaking. Instead, they held on to the shelves and tried to stop the goods (货物) from falling down.

     Reporters from NHK, the country's largest TV station, stayed calm in front of cameras during the earthquake, even though some were facing real danger.

     The earthquake was the most powerful one to hit Japan in the country's history. But Japan's reaction

(反应) to the accident has shown that it is the most earthquake-prepared country in the world. The calm the

Japanese showed during and after the quake has impressed the world. This is because Japan has "an earthquake

culture". Japanese people are taught how to prepare for and react to earthquakes from a young age.

     Schools in Japan organize earthquake practices every month. They make students become familiar with

being in an earthquake.

     Japan also has a good earthquake warning system (警报系统). Warnings were broadcast on television,

radio and mobile phones nine seconds after experts (专家) first knew about the quake on March 11.

     The warning system is unable to predict earthquakes. But it can usually alert people about 15 seconds

before they feel the effects. Even 15 or 20 seconds can be enough time to save people's lives.

1. How did Japanese people react when the big earthquake hit Japan on March 11?

A. They felt angry.

B. They were scared.

C. They stayed calm.

D. They were frustrated.

2. Which of the following is TRUE according to the passage?

A. Japan's reaction to the earthquake impressed the world.

B. Japanese schools organize earthquake practice every day.

C. Japan has a warning system that can predict earthquakes.

D. Japanese people learn about earthquake safety only from universities.

3. After experts first knew about the quake on March 11, warnings were not broadcast ________.

A. on radio

B. on the movie

C. on television

D. on mobile phones

4. What does the underlined word "alert" mean in Chinese?

A. 改善

B. 提高

C. 提醒

D. 改变

5. What does the story mainly tell us about?

A. Japan's earthquake culture.

B. The bad results caused by the earthquake.

C. Japanese people were scared after the earthquake.

D. Japanese people were homeless after the earthquake.

单项选择题