问题 选择题

关于相互接触的两物体之间的弹力和摩擦力,下列说法正确的是(  )

A.有摩擦力一定有弹力

B.有弹力一定有摩擦力

C.摩擦力与弹力成正比

D.弹力是动力摩擦力是阻力

答案

A、摩擦力产生的条件中,必须接触挤压,所以有摩擦力必有弹力.故A正确.

    B、有弹力不一定有摩擦力,还需有相对运动或相对运动的趋势.故B错误.

C、滑动摩擦力的大小与正压力成正比,静摩擦力大小与压力无关.故C错误.

D、一个力是动力还是阻力,看该力与运动的方向相同还是相反.摩擦力的方向可能与运动方向相同,可以是动力.故D错误.

故选A.

阅读理解

阅读理解。

     How many people have I met who have told me about the book they have been planning to write but have

never yet found the time? Far too many.

     This is Life, all right, but we do treat it like a rehearsal (排演) and, unhappily, we do miss so many of its

best moments.

     We take jobs to stay alive and provide homes for our families always making ourselves believe that this

style of life is merely a temporary state of affairs along the road to what we really want to do. Then, at 60 or

65, we are suddenly presented with a clock and several grandchildren and we look back and realize that all

those years waiting for Real Life to come along were in fact real life.

     In America they have a saying much laughed at by the English: "Have a nice day" they speak slowly and

seriously in their shops, hotels and sandwich bars. I think it is a wonderful phrase, reminding us, in effect, to

enjoy the moment: to value this very day.

     How often do we say to ourselves, "I'll take up horse-riding (or golf, or sailing) as soon as I get a higher

position," only to do none of those things when I do get the higher position.

     When I first became a reporter I knew a man who gave up a very well paid respectable job at the Daily

Telegraph to go and edit a small weekly newspaper. At the time I was astonished by what appeared to me to

be his completely abnormal (反常的) mental state. How could anyone turn his back on Fleet Street in central

London for a small local area?I wanted to know.

     Now I am a little older and possibly wiser, I see the sense in it. In Fleet Street the man was under continual

pressure. He lived in an unattractive London suburb and he spent much of his life sitting on Southern Region

trains.

1. The first paragraph of the passage tells us that _____.

A. we always try to find some time to write a book

B. we always make plans but seldom fulfill them

C. we always enjoy many of life's best moments

D. we always do what we really want to do

2. The underlined phrase "turn his back on" (paragraph 6) most probably means _____.

A. leave for

B. return to

C. give up

D. rely on

3. The man ( paragraph 6) left his first job partly because he was _____.

A. in an abnormal mental state

B. under too much pressure

C. not well paid

D. not respected

4. What is probably the best title for the passage?

A. Provide Homes For Our Family

B. Take Up Horse-riding

C. Value This Very Day

D. Stay Alive

单项选择题