问题 计算题

能源短缺和环境恶化已经成为关系到人类社会能否持续发展的大问题。为缓解能源紧张压力、减少环境污染,汽车制造商纷纷推出小排量经济实用型轿车。某公司研制开发了某型号小汽车发动机的额定功率为24 kW,汽车连同驾乘人员总质量为m=2 t,在水平路面上行驶时受到的阻力是800 N,求:

(1)汽车在额定功率下匀速行驶的速度;

(2)汽车在额定功率下行驶,速度为20 m/s时的加速度。

答案

(1)30 m/s (2)0.2 m/s2

题目分析:(1)汽车匀速运动时,牵引力等于阻力,F=f=800N

根据P=mv解得:v=30m/s

(2)设当速度为20m/s时的牵引力为F,则

根据牛顿第二定律得

点评:本题难度较小,当汽车速度最大的时候牵引力等于阻力,速度达到最大

阅读理解

     Young people and older people do not always agree with each other. They sometimes have different

ideas about living, working and playing. But in one special program in New York State, adults and

teenagers live together in a friendly way.

     Each summer 200 teenagers and 50 adults live together for eight weeks as members of a special work group. Everyone works several hours each day. They do so not just to keep busy but to find meaning and enjoyment in work. Some teenagers work in the woods or on the farms near the village. Some learn to

make things like tables and chairs and to build houses. The adults teach them these skills.

     There are several free hours each day. Weekends are free, too. During the free hours some of the

teenagers learn photo-taking or painting. Others sit around and talk or sing. Each teenager chooses his

own way to spend his free time.

     When people live together, rules are necessary. In this program, the teenagers and the adults make

the rules together. If someone breaks a rule, the problem goes before the whole group. They talk about it

and ask, "Why did it happen? What should we do about it?"

     One of the teenagers has this to say about the experience, "You stop thinking only about yourself. You

learn how to think about the group."

1. In one special program in New York, young and older people ______.

A. are friendly to each other.

B. teach each other new ways of building houses

C. live together but do not work together

D. spend eight weeks together, working as farmers

2. Living together, ________.

A. the teenagers have to obey the rules the adults make

B. the members don't have to obey the rules

C. the members are not allowed to break the rules they make together

D. the members have no free time except on weekends

3.The last paragraph shows that the teenager thinks his experience in the program is _____.

A. disappointing    

B. helpful      

C. tiring  

D. unpleasant

4. The best title for the passage is _______.

A. Rules of Living Together        

B. Different Ideas about Living

C. Teenagers and Adults Together    

D. Life in New York State

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