问题 计算题

如图所示,在一条小河中有一条小船,船受到一个与河岸成30°角的拉力F=1000 N的作用。要使船沿与河岸平行的方向前进,需要另加一个力的作用,则这个力向什么方向最省力?该力的大小为多少?

答案

解:若使船沿平行河岸方向前进,所加力与原力F的合力方向应平行于河岸,这有无数种情况,如图所示画出了其中的三种

由图中的几何关系可知,只有当所加的力垂直于河岸时,才最省力

解直角三角形:F1=Fsin30°=1000 N×=500 N,方向垂直于河岸向下

单项选择题
阅读理解

阅读理解。

     As a young man,Al was a skilled artist,a potter (陶工). He had a wife and two

fine sons. One night, his elder son developed a serious stomachache. Thinking it was

only some common disorder, neither Al nor his wife took the condition very seriously.

But it was actually acute appendicitis (急性阑尾炎), and the boy died suddenly that

night.

     Knowing the death could have been prevented if he had only realized the seriousness

of the situation, Al's emotional health deteriorated (恶化) under the burden of his guilt.

To make matters worse, his wife left him a short time later, leaving him alone with his

sixyearold younger son. The hurt and pain of the two situations were more than Al could

handle,and he turned to alcohol to help him cope. In time Al became an alcoholic (酒鬼).

     As the alcoholism progressed,Al began to lose everything he possessed-his home, his

land and his art objects. Eventually Al died alone in a San Francisco motel room.

     When I heard of Al's death,I reacted with the same disdain (蔑视) the world shows for

one who ends his life with nothing to show for it. "What a complete failure!" I thought. "What

a totally wasted life!"

     As time went by, I began to reevaluate my earlier judgment. I knew Al's now adult son,

Ernie. He has grown into one of the kindest, most caring and most loving men I have ever

known. I watched Emie with his children and saw the free flow of love between them. I knew

that kindness and consideration had to come from somewhere.

     I hadn't heard Ernie talk much about his father. One day I worked up my courage to ask

him. "I'm really puzzled by something," I said. "I know your father was basically the only one

to raise you. What on earth did he do to make you become such a special person?"

     Ernie sat quietly and reflected for a few moments. Then he said, "Al came into my room

every night,gave me a kiss and said 'I love you,son' until I left home at 18."

     Tears came to my eyes as I realized what a fool I had been to judge Al as a failure. He had

not left any material possessions behind. But he had been a kind and loving father, and he was

one of the finest men I have ever known.

1. Al's elder son probably died of acute appendicitis due to ________ according to this passage.

A. lack of care and nutrition                      

B. the couple's carelessness

C. serious stomachache          

D. too much alcohol

2. What can we know from the second paragraph?

A. Given more attention, the boy could be saved.

B. Al eventually became an alcoholic without any reason.

C. Al's wife was also dead because of her elder son's death.

D. The boy's death couldn't be avoided even if he was given more attention.

3. In the writer's opinion, what was Al like?

A. Careless.                

B. Foolish.              

C. Bad.                    

D. Familyloving.

4. How did the writer evaluate Al's son, Ernie in this passage?

A. Kind.                  

B. Caring.              

C. Loving.                

D. All above.

5. The purpose of writing this passage for the writer is to show ________.

A. we should reevaluate Al's meaning of life      

B. love is the best heritage in our life

C. Ernie is a kind, caring and loving son          

D. Al's death is a totally wasted life as well