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问题 计算题

（15分）汽车发动机的额定功率为60kW，汽车的质量为5×103 kg，运动中所受阻力的大小恒为车重的0.1倍。

（1）若汽车以恒定功率启动，汽车所能达到的最大速度是多少?当汽车速度达5m／s时的加速度多大?

（2）若汽车以恒定加速度0.5m／s2启动。则这一过程能维持多长时间?

答案

（1）12m/s     1.4m/s2          （2）16s

题目分析：（1）最大速度时牵引所F大小等于阻力f

根据，得

当速度达到5m／s时，牵引力

根据牛顿第二定律

因此加速度

（2）若汽车以恒定加速度0.5m／s2启动

根据牛顿第二定律，

牵引力

根据，可知达到额定功率时的速度

根据，可得加速的时间

选择题

—I have tried very hard to find a solution to the problem, but in vain.

—Why not consult with Frank? You see, ________.[ ]

A. great minds think alike

B. two heads are better than one

C. a bird in the hand is worth two in the bush

D. it's better to think twice before doing something
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填空题

Part 1


·Read thefollowingpassage, eight sentences have been removed from the article.
·Choose from the sentences A-H the one whichfits each gap.
·For each gap (1-8) mark one letter (A-H) on the Answer Sheet.
·Do not mark any letter twice.
The single, decisive factor that made it possible for mankind to settle in permanent communities was agriculture. (1) Once people could control the production of food and be assured of a reliable annual supple of it, their lives changed completely.
Fanning was a revolutionary discovery. (2) With more food available, more people could be fed. Populations therefore increased. The growing number of people available for more kinds of work led to the development of more complex social structures. (3)
Farming the world over has always relied upon a dependable water supply. For the earliest societies this meant rivers and streams or regular rainfall. (4) Later communities were able to develop by taking advantage of the rainy seasons.
All of the ancient civilizations probably developed in much the same way, in spite of regional and climatic differences. (5) Heavier pottery replaced animal-skin gourds as containers for food and liquids. Cloth could be woven from wool and flax. Permanent structures made of wood, brick, and stone could be erected.
The science of mathematics was an early outgrowth of agriculture. People studied the movements of the moon, the sun, and planets to calculate seasons. (6) With a calendar it was possible to calculate the arrival of each growing season. Measurement of land areas was necessary if property was to be a factor in farming and housekeeping. (7) All of the major ancient civilizations in Mesopotamia, Egypt, the Indus Valley, and China emerged in the 4th millennium BC. Historians still debate over which one emerged first. It may well have been the Middle East, in an area called the Fertile Crescent. This region stretches from the Nile River in Egypt northward along the coast of former Palestine, then eastward into Asia to include Mesopotami
  • a. (8) This kind of larming depended on the reproduction of seed, normally from grain crops.A. It not only made settlements possible and ultimately the building of cities but it also made available a reliable food supply.B. Later came measures of value as commodity and money exchange became common.C. In this area people settled along the riverbanks and practiced field agriculture.D. After farming was developed in the Middle East in about 6500 BC, people living in tribes or family units did not have to be on the move continually searching for food or herding their animals.E. As villages grew, the accumulation of more numerous and substantial goods became possible.F. With a food surplus, a community could support a variety of workers who were not farmers.G. The first great civilizations grow up along rivers.H. In doing so they created the first calendars.
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