问题 计算题

近年来,汽车逐步走进了普通百姓的家庭。如图17所示是一辆小轿车的一些参数,请根据这些数据完成下列问题:(取g=10N/kg)

整车质量(kg)1500排量(L)2.0
最大功率(kW)130最高车速(km/h)200

(1)汽车受到的重力是多少?若每个车轮与地面的接触面积为0.05m2,则它对地面的压强是多少?(3分)

(2)汽车以最高车速匀速前进了200km,发动机对汽车所做的功是多少?汽车所受到的牵引力是多少?(发动机在最大功率时汽车的速度最大)(4分)

答案

(1)15000N, 3×105Pa

(2)t=1h,w=pt=4.68×108J,F=234000N

分析:(1)由表格中数据可知汽车的质量,则由重力公式可求得汽车的重力;由压强公式可求得汽车对地面的压强;

(2)汽车以最大速度行驶,则功率应达到最大值,则由功的公式可求得发动机对汽车所做的功;由W=Fs可求得汽车受到的牵引力.

解答:解:(1)由表格可知,汽车的质量m=1500kg;则其重力G=mg=1500kg×10N/kg=15000N;

汽车对地面的压力F=G;

则压强P==7.5×104Pa;

(2)t=1h=3600s;

发动机对汽车所做的功W=pt=130w×3600s=4.68×108J;

由W=Fs′可得:

F==2340N;

答:(1)汽车的重力为15000N;汽车对地面的压强为7.5×104Pa;(2)发动机对汽车所做的功为4.68×108J;汽车受到的牵引力为2340N.

完形填空

Today there are policemen everywhere, but in 1700, London had no policemen at all. A few old men used to protect the city streets at night and they were not paid.

About 300 years ago, London was starting to get bigger and more and more people began to live there. The city was very dirty and many people were poor. (93). There were so many thieves who stole money in the streets that people stayed in their homes as much as possible.

In 1750, Henry Fielding started to pay a group of people to stop thieves. They were like policemen and were called "Bow Street Runners" because they worked near Bow Street.

Fifty years later, there were 120 "Bow Street Runners", but London had become very big and needed more policemen. So in 1829, the first Metropolitan (or London) Police Force was started with 3,000 officers. Most of the men worked on foot, but a few rode horses. Until 1920 all the police in London were men.

(94). Today, London police are quite well paid, especially for the few police officers who still ride horses, the pay is even better than for the others.

A.根据短文内容简要回答下列问题:

小题1:Why did people stay in their homes as much as possible about 300 years ago?

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小题2:When was the first London Police Force started with 3,000 officers?

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B. 将短文中划线的两个句子译成汉语。

小题3:________________________________________________________

小题4:________________________________________________________

小题5:请给短文拟一个适当的英文标题_______________________________

填空题