试题与答案

某单缸四冲程汽油机的气缸活塞面积为30cm2,一个冲程活塞在气缸中移动的距离是5

题型:计算题

题目:

某单缸四冲程汽油机的气缸活塞面积为30cm2,一个冲程活塞在气缸中移动的距离是50mm,满负荷工作时做功冲程燃气的平均压强为9.0×l05Pa,飞轮lmin转动1800周,当汽油机满负荷工作时(不计摩擦),若1min消耗汽油0.01L.汽油的密度ρ=0.8×103kg/m3;汽油的热值为4.6×l07J/kg.求:

(1)做功冲程中燃气对活塞的平均压力;

(2)一个做功冲程中燃气对活塞做的功;

(3)汽油机的功率.

(4)该汽油机的效率.

答案:

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参考答案:D解析:由题意知,以前研究认为"食用巧克力会增加食用者患心脏病的可能性"。新结论是:"食用巧克力与心脏病发病率无关"。只有假设D项成立,才能推出"研究成果公布后,巧克力的消费量将会大大增加"的结...

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题型:阅读理解

       Chinese are very generous(大方的) in educating their children. Not caring about the money, parents

often send their children to the best schools or even abroad to England, the United States and Australia.

They also want their children to take extra-course activities such as musical instrument learning or ballet  

classes, or other classes. They think these will give them a good future. The Chinese believe that the more expensive an education is, the better it is. So parents will spend much unreasonable(不 理智的 ) money on education. Even poor parents will buy a computer for their son or daughter.

                                             

       However, most parents don't understand that the best early education they can give their children is

usually very cheap.

       Parents can see that their children are very good in some areas while poor in others. Parents also

can see some children are good at these skills and others do well in others. Most parents don't realize

that today's children lack self-respect and self-confidence(自信).

       The problem is that parents are only educating their children on how to take tests and how to study

well, but parents are not teaching them the most important skills that they need to be confident, happy

and clever.

       Parents can achieve this by teaching skills like cooking, sewing and doing other housework. Teaching a child to cook will improve many of the skills that he will need later in life. Cooking needs patience and

time. It is an enjoyable but difficult experience. A good cook always tries to improve his cooking, so he

will learn to work hard and finish his job successfully. His result, a well-cooked dinner, will give him much

satisfaction and lots of self-confidence.

       Some old machines, such as a broken radio or TV set that you give your child to play with will make

him curious and improve his interest. He will spend hours looking at them, trying to fix them. Your child

might become an engineer when he grows up. These activities are not only teaching a child to read a book, but rather to think, to use his mind. And that is more important.

1. What don't most parents realize today ?  

A. Education is very important to children.

B. Today's children lack self-respect and self-confidence.

C. Today's children lack of skills for tests.

D. Taking extra-courses is useful for children's future.

2. Generally speaking, children's skills __________.

A. come from their parents            

B. have nothing to do with their education

C. may be different from child to child  

D. have much to do with their marks in the exams

3. Doing some cooking at home helps children_________.

A. learn how to help their parents    

B. learn how to become strong and fat

C. learn to work hard and be full of confidence  

D. make their parents believe that they are clever

4. The writer of this passage don't agree with_______.

A. the parents' ideas of educating children    

B. the country's education system

C. the children's skills                    

D. the children's hobbies

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