问题 选择题

小刚站在台秤上称体重,在下列各对力中属平衡力的是(  )

A.小刚的重力和台秤对他的支持力

B.小刚对台秤的压力和台秤对他的支持力

C.台秤的重力和台秤对小刚的支持力

D.小刚的重力和他对台秤的压力

答案

A、小刚受到的重力与台秤对他的支持力符合二力平衡的条件,故A正确;

B、小刚对台秤的压力和台秤对它的支持力为作用在相互作用的两个物体上,故为作用力与反作用力,故B错误;

C、台秤的重力和台秤对小刚的支持力,分别作用在台秤上和小刚身上,不符合二力平衡的条件,故C错误;

D、小刚的重力和他对台秤的压力为作用两个物体上的力,故不符合二力平衡的条件,故D错误;

故选A.

解答题
阅读理解

阅读理解。

     BEIJIN-No Car Day was first started by 34 cities in France on September 22,1998. It was started to

protect the environment, By now, more than 1,000 cities around the world have had a No Car Day.

     The first No Car Day in China was in Chengdu in 2001.Other cities,including Taipei, Shanghai and Wuhua,

also support the day.

     In Beijing, more and more people are joining in the activity. It asks the drivers to leave their cars at home

for one day each month and walk or ride a bike to work. It also calls on Beijingers not to use cars on June 5

(World Environment Day). The slogan (口号) for the day is, "If we drive for one less day, we can have one

more nice day."

     So far, more than 200,000 drivers have shown their support."We can't control the weather, but we can

choose not to drive.'' said, Wu Zonghua, a car club chairman. Beijing is trying to have 238 blue sky days this

year. In the first quarter of this year, Beijing only had 52 blue sky days. This was 11 days less than the number

for the same period last year. Much of the dust comes from the desert,but cars cause most of the air pollution. We must do more for No Car Day.

1. There are _______ cities in China that support No Car Day according to the passage.

A. three

B. four

C. five

D. six

2. The activity of No Car Day encourages Beijing drivers _______.

A. not to work on No Car Day

B. to enjoy having a day off

C. to leave their cars at home for repair

D. to ride a bike or walk instead of driving to work

3. According to the passage there were _______ blue sky days in the first quarter of last year in Beijing.

A. 52

B. 63

C. 41

D. 238

4. The air pollution in Beijing is mostly caused by _______.

A. cars

B. dust

C. weather

D. rubbish

5. We can know from the passage that _______.

A. more and more people in Beijing are joining car clubs

B. people will have one more World Environment Day each month

C. more and more people won't drive on Nor Car Day in Beijing

D. more people in the world won't drive any more