问题 选择题

如图所示,斜面体放置在水平地面上,物块沿粗糙的斜面加速下滑,斜面体始终保持静止,在此过程中(   )

A.斜面体对物块的作用力斜向左上方

B.斜面体对物块的作用力斜向右上方

C.地面对斜面体的摩擦力水平向右

D.地面对斜面体的支持力大于物块与斜面体的重力之和

答案

BC

题目分析:由于物块沿粗糙的斜面加速下滑,其加速度的方向沿斜面向下,故其受到的合力也是沿斜面向下,物块受到重力是竖直向下的,所以斜面对物块的力只有斜向右上方,它与重力的合力才可能沿斜面向下,故A不对;B是正确的;

如果将斜面与物块看成一个整体,则其整体的加速度方向是向右下方的,故地面对斜面体的摩擦力方向水平向右,C是正确的;看成一个整体时,其受到的合力在竖直方向上是向下的,故地面对斜面体的支持力会小于物块与斜面体的重力之和,D是不对的;

阅读理解

阅读理解。

     Long ago in a small town, there was a place known as the House of 1,000 Mirrors. A small, happy

little dog learned of this place and decided to visit.

     When he arrived, he bounced (跳) happily up the stairs to the doorway of the house. He looked

through the doorway with his ears lifted high and his tail wagging as fast as it could. To his great surprise,

he found himself staring at 1,000 other happy little dogs with their tails wagging just as his. He smiled a

great smile, and was answered with 1,000 great smiles just as warm and friendly. As he left the house, he

thought to himself, "This is a wonderful place. I will come back and visit often."

    In this same village, another little dog, who was not quite as happy as the first one, decided to visit the

house. He slowly climbed the stairs and hung his head low as he looked into the door. When he saw the 1,000 unfriendly looking dogs staring back at him, he growled at them and was horrified to see 1,000

little dogs growling back at him. As he left, he thought to himself, "This is a horrible place, and I will never

go back there again."

     All the faces in the world are mirrors. What kind of reflections do you see on the faces of the people

you meet?  

1. Why was the first dog surprised when he entered the house?

A. Because he didn't expect to see so many happy dogs.

B. Because he didn't know there were 1,000 mirrors in the house.

C. Because he was always in a mixed mood.

D. Because he saw so many dogs smiling at him.

2. Why did the first dog like the house?

A. Because there were 1,000 mirrors in the house.

B. Because he thought he could keep himself warm in the house.

C. Because he liked everything presented to him.

D. Because he felt he was welcome here.

3. The underlined word "growl" probably means ______.

A. make an unfriendly noise                    

B. smile    

C. say hello                                  

D. stare

4. Which of the following is the most suitable title for the passage?

A. A Small happy Little Dog                    

B. The House of 1,000 Mirrors

C. The Wonderful Place and the Horrible Place.  

D. Two Little Dogs

单项选择题