问题 问答题

有一卷无木轴的铜导线,需要确定它的长度,但不能把铜导线全部拉开,更不能把导线截断,请设计一个测量方案(提出使用器材,说明测量步骤,给出计算方法.)器材:铅笔一只,刻度尺一把(游标卡尺等其它尺也行),能称量导线质量的任何形式的秤一个.

答案

答:测量步骤:

(1)拉出一段导线,在铅笔上绕n圈,测出总长度L,铜导线直径d=

L
n

(2)用称称出导线的总质量m;

(3)铜导线的体积体积:V=Sl=πr2l=π(

d
2
)2l=
πd2l
4
=
πl(
L
n
)2
4
=
πlL2
4n2
  ①;

(4)∵ρ=

m
V
,∴铜导线的体积V=
m
ρ
  ②,由①②解得,铜导线的长度l=
4n2m
πρL2
,ρ是铜的密度.

阅读理解

阅读理解。

       A man was selling medicines at a fair (集市). At first he sold bottles of a cure (药) for colds for just a dollar

a bottle.

       Many people wanted to buy it and the man's young assistant moved quickly through the crowd collecting

money and handing out bottles of the cold cure.

       Then, when he had a big crowd, the man held up a very small bottle.

       "And now, ladies and gentlemen," he shouted, "here is the medicine you have been waiting for. The cure for

old age. Drink just one bottle of this and you will live forever."

       "And, ladies and gentlemen," the man continued, "I'm not going to charge (收费) you a hundred dollars a

bottle for this wonderful medicine. I'm not going to charge you fifty dollars a bottle. I'm not going to charge you

twenty-five dollars a bottle. No, ladies and gentlemen, I'm going to charge you just ten dollars a bottle. Think,

my friends, for ten dollars you can live forever." 

        Most of the people in the crowd did not believe this.

        One person shouted, "If it will make you live forever, why don't you drink it?" 

        Then another person cried, "Yes, you look as if you're at least sixty years old."

        "Thank you, sir, thank you," the man replied. "I'm so glad you said that. My real age is three hundred and

twenty-nine." 

        The crowd laughed at this, but there were still a few people who wanted to believe the man. One of them

spoke to the man's assistant as she passed by. "Is it true" he asked, "that he's three hundred and

twenty-nine?" 

        "Don't ask me," the assistant said. "I've only worked for him for a hundred and fifty years."

1.What did the man sell at first? [ ]

A.A cure for colds.

B.Empty bottles.

C.A cure for old age.

D.A medicine that made people live forever.

2.Why didn't the people believe the man was selling medicine that could cure (治病) old age? [ ]

A.The medicine was too cheap.

B.The medicine was too expensive.

C.He looked quite old himself.

D.He didn't look honest.

3.How old did the man selling medicine say he was? [ ]

A.At least sixty.

B.Over three hundred.

C.A hundred and fifty.

D.He didn't say.

4.How much did the man charge for the cure for old age? [ ]

A.One dollar a bottle.

B.Twenty-five dollars a bottle.

C.Ten dollars a bottle.

D.Fifty dollars a bottle.

5.Which of the following is TRUE? [ ]

A.Not very many people wanted to buy the cold cure.

B.He charged twenty-five dollars a bottle for the cure for colds.

C.The man selling medicine had taken his own cure for old age.

D.The assistant was younger than the man.

选择题