问题 选择题

如图所示,物体在长度相等的细绳AO、BO的作用下处于静止状态,现将B点向右移动一小段距离,重新平衡后,则(  )

A.两绳的拉力的合力变大

B.两绳的拉力的合力不变

C.AO绳的拉力与重力的合力变小

D.BO绳的拉力与重力的合力不变

答案

A、B、对点O受力分析,受重力和两个拉力,如图

设两个拉力的夹角为θ,根据图象得到:

FA=FB=

2mg
cos
θ
2

故当B点向右移动一小段距离,角θ变大,两个拉力都变大;

两个拉力的合力与重力等值、反向、共线,故两个拉力的合力不变,故A错误,B正确;

C、AO绳的拉力与重力的合力与BO绳的拉力等值、方向、共线,由于BO绳的拉力变大,故AO绳的拉力与重力的合力变大,故C错误;

D、BO绳的拉力与重力的合力与AO绳的拉力等值、方向、共线,由于AO绳的拉力变大,故BO绳的拉力与重力的合力变大,故D错误;

故选B.

单项选择题 A1型题
阅读理解

阅读理解。

     Last week my youngest son and I visited my father at his new home in Tucson, Arizona. He moved there

a few years ago, and I was eager to see his now place and meet his friends. My earliest memories of my father

are of a tall, handsome, successful man devoted to his work and family, but uncomfortable with his children.

As a child I loved him; as a school girl and young adult (成年人) I feared him and felt bitter about him. He

seemed unhappy with me unless I got straight A's and unhappy with my boyfriends if their fathers were not

as "successful" as he was. Whenever I went out with him on weekends, I used to struggle to think up things

to say, feeling on guard.

     On the first day of my visit, we went out with one of my father's friends for lunch at an outdoor cafe. We

walked along that afternoon, did some shopping, ate on the street table, and laughed over my son's funny facial

expressions. Gone was my father's critical (挑剔的) air and strict rules. Who was this person I knew as my

father, who seemed so friendly and interesting to be around? What had held him back before?

     The next day, my dad pulled out his childhood pictures and told me quite a few stories about his own

childhood. Although our times together became easier over the years, I never felt closer to him at that moment

. After so many years, I'm at last seeing another side of my father. And in so doing, I'm delighted with my new

friend. My dad, in his new home in Arizona, is back to me from where he was.

1. Why did the author feel bitter about her father as a young adult?

A. He was silent most of the time.

B. He was too proud of himself.

C. He did not love his children.

D. He expected too much of her.

2. When the author went out with her father on weekends, she would feel _____.

A. nervous

B. sorry

C. tired

D. safe

3. What does the author think of her father after her visit to Tucson?

A. More critical. 

B. More talkative.

C. Gentle and friendly.

D. Strict and hard-working.

4. The underlined words "my new friend" in the last paragraph refer to _____.

A. the author's son

B. the author's father

C. the friend of the author's father 

D. the cafe owner