问题 选择题

关于力和运动的关系,以下说法中正确的是

A.物体受到外力作用,其速度大小一定改变

B.物体受到恒定的合外力作用,其加速度一定不变

C.物体做曲线运动,说明其受到合外力为变力

D.物体做匀速圆周运动,其受到的合外力为恒力

答案

答案:B

题目分析:物体受到非平衡力一定改变运动状态,物体受到平衡力时,运动状态不会发生改变.所以A错误;物体受到不变的合外力的作用,根据牛顿第二定律可知,其加速度也是不变的,所以B正确;物体做曲线运动的条件是合力与速度不在同一条直线上,合外力大小和方向不一定变化,比如平抛运动,此时物体受到的就是恒力的作用,所以C错误;匀速圆周运动受到的合力作为向心力,始终是指向圆心的,所以此时受到的合力一定是变力,所以D错误;

故选B.

点评:解决本题的关键知道加速度的方向与合力的方向相同,以及掌握判断物体做直线运动还是曲线运动的方法.

单项选择题
阅读理解

B

In China, if you are not married by the time you are 30, you are in for trouble: social blame and pressure from family and friends can get you down. And if you are a woman it’s even worse.

Many young people get married simply to get other people off their backs(免受别人的指责) . This is a serious compromise (妥协) with their ideals (理想). One ends up not marrying the ideal partner.

There are, however, a few young people who refuse to compromise: if they can’t find a good marriage partner,they say, they would rather not many at all.

34-year-old Kate is university lecture in English.She said she would not describe herself as backelorette(独身主义者) but simply a woman who hasn't come across the right man yet. She has sharp comments for the way in which the old generation looks at marriage.

“Many people think marriage is a duty —— to your parents, family and society. Nobody cares if your marriage is happy or not. she said, I think this is very wrong and I intend to live and act according to my own will.”

Happily for her, her parents are open-minded and not put pressure on her. But the same does not apply to her friends. They are .constantly trying to get her together with some young man or another. She always refuses politely.

59. The main idea of this passage is that ____ .

A. marriage is duty to society

B. people should get married before 30 years old

C. late marriage should be respected

D. women should get married earlier than men

60. Miss Kate refuses to get together with some young man or another because____.

A. she doesn’t think he is the right man she wants

B. he is either too old or too young

C. he is either important or little learned

D. he doesn’t have good manners

61. In the first paragraph the underlined words “in for”  refer to ____.

A. interested in   B. satisfied with    C. worried about   D. possible to suffer

62. Which is not true according to this passage

A. In China, one mil face social blame and family pressure if one hasn’t got married at he age of 30.

B. Miss Kate’s parents are always worried about her marriage.

C. Miss Kate won’t compromise with her ideal marriage.

D. Miss Kate wants to many a worthy young man.

63. If marriage is regarded as a duty to society,_______.

A. everybody will be happy and satisfied

B. nobody will pay attention to whether you are happy or not in your family life

C. you can easily find an ideal partner

D. young people will have nothing to worry about in marriage