问题 选择题

如图11-3-所示,物体A置于物体B上,一轻质弹簧一端固定,另一端与B相连,在弹性限度范围内,A和B一起在光滑水平面上做往复运动(不计空气阻力),并保持相对静止.则下列说法中正确的是(    )

图11-3

A.A和B均做简谐运动

B.作用在A上的静摩擦力大小与弹簧的形变量成正比

C.B对A的静摩擦力对A做功,而A对B的静摩擦力对B不做功

D.B对A的静摩擦力始终对A做正功,而A对B的静摩擦力始终对B做负功

答案

AB

将A B看作一个整体,可知其运动为简谐运动,A选项正确.B对A的静摩擦力提供A的回复力,通过隔离法可知,其大小也与弹簧的形变量成正比,故B选项正确.运动过程中,A对B的静摩擦力在水平方向上有位移,从而做功,故C选项错误.A的动能变化是通过B对A的静摩擦力对A做功实现的,A的动能有时增大有时减小,依据动能定理可知,B对A的静摩擦力对A有时做正功,有时做负功,故D选项错误.

选择题
阅读理解

阅读理解。

     On April 24th , another natural disaster - the oil spill(泄露)in the Gulf of Mexico , happened .

Millions of dollars have been used to help stop the spill and to clean up the animals , beaches , and

land spoiled by the oil . Unfortunately , when many of these chemicals are used , more damage is

caused to the environment , especially to lives in the sea .

     But governments seem to accept the risk of transporting millions of tons of oil by ship every day

so that we can fill up our cars and drive around and cause even more environmental damage .

 Interestingly , the biggest companies in the world produce cars , and the next biggest supply the

gasoline to make them run .

     Of all of today's environmental disasters , an oil spill may actually be one of the least serious .

Although oil is poisonous , it is a natural material . In the end , it breaks down naturally . In 1967

the tanker Torrey Canyon sank off the Scilly Isles near the coast of England and spilled 120,000

tones of oil into the ocean . If you go there today , you will find it hard to see any sign that it ever

happened .

     However , we should be thinking more about reducing our dependency on oil . Governments

should be encouraging research into new technologies , such as cars run by solar power, electricity ,

hydrogen , and so on . Much of this research , in the past , was stopped by the oil , gas , and coal .

If the world's millions of cars were 10% more efficient(高效的), we would need many fewer tankers

crossing the oceans each year . If this happened , the risks of oil spills would be reduced , and the air

we breathe would be cleaner and fresher , too .

1. What is the passage mainly talking about ?

A. Oil spills pollution                

B. What oil pollution is

C. Oil tanker accidents              

D. How to reduce oil pollution

2. How does the author support the idea that oil spills are not as serious as people believe ?

A. By giving a description            

B. By making an argument

C. By giving an example            

D. By drawing a diagram(图表)

3. What does the underlined word " risk " in Paragraph 2 refer to ?

A. Transportation depending more on oil

B. Poisonous oil breaking down naturally

C. Millions of tons of oil spilling into the sea

D. More environmental damage being caused

4. Which suggestion is made for reducing oil tank according to the passage ?

A. We should build safer tankers in the near future

B. We should develop new technologies to cut oil use

C. Tankers should not be allowed to sail near the coastlines

D. Countries should build more oil pipelines under the sea

5. Where can you read this article ?

A. In a story book .              

B. In a science magazine .

C. In a novel                    

D. In a brochure .