问题 问答题

学习了功的知识后,章莹和爱萍同学就“人们为什么要使用简单机械”进行了讨论、她们想:使用机械有时可以省力,有时能够省距离,那么使用机械可不可以省功呢?带着这个问题,她们去问老师、老师却给她们提供了一根细线、一段绳子及动滑轮、铁块、铁架台各一只,要她们自己去验证、以下是她们的探究过程,请帮助她们完成下面的填空、

(1)老师少给了她们一样必要的器材,这件器材是______.

(2)她们用细线系住铁块,并用向老师要来的器材测出铁块的______.

(3)用手直接将铁块竖直向上匀速提升20cm,求出这次对铁块所做的功是W1

(4)再利用动滑轮将这个铁块也竖直向上匀速提升20cm,测出这时绳子自由端的拉力是1.5N、那么这次拉力所做的功W2=______J.

(5)经过比较,她们发现W2>W1,请你和她们一起分析造成W2>W1的一种可能的原因是______.

(6)她们将所得到结论告诉老师向老师求证,老师告诉她们,只要方法正确,无论用哪种机械进行实验,都有这样的规律:把同一物体匀速提升相同高度的条件下,使用机械时做的功大于直接用手对物体做的功、即“使用任何机械都______省功”(填“能”或“不能”).

答案

(1)在探究使用机械可不可以省功问题时,若用动滑轮提升重物进行实验,必须用弹簧测力计测出物体的重力和自由端的拉力;

故答案为:弹簧测力计.

(2)需要测出铁块的重力;

故答案为:重力

(4)绳子自由端移动的距离为s=20cm×2=40cm=0.4m,拉力做的功W2=Fs=1.5N×0.4m=0.6J;

故答案为:0.6.

(5)用动滑轮提升铁块时,动滑轮也跟着铁块升高,所以要克服动滑轮重力做功,而且还要克服摩擦力做额外功,所以一定有W2>W1

故答案为:必须克服动滑轮重及摩擦力做一些额外功.

(6)把同一物体匀速提升相同高度的条件下,使用机械时做的功大于直接用手对物体做的功,所以使用任何机械都不能省功;

故答案为:不能.

阅读理解

阅读理解。

     The time of year a baby is born can shape what profession they will embark on(从事) in later life,

a new study has suggested.

     Being born in a certain month appears to indicate the statistical likelihood of what job a person wil

l end up with, the study by the Office for National Statistics found.

     Researchers have uncovered that the month in which babies are born could also affect everything

from intelligence to length of life.

     A child born December is more likely to become a dentist while someone whose birthday falls in

January will tend to a debt collector, they found. A February birth appears to increase the chances

of being an artist while March babies appear to go on to become pilots. Meanwhile, April and May

are said to have a fairly even spread of professions, births in the summer months mean a much lower

chance of becoming a high-earning football player, doctor or dentist.

    The study was got by researchers who analyzed the birth months of people in 19 separate occupations

using information from the last survey, the Daily Mail reported. Although these trends may be difficult

to explain, correlations between birth months and specific health problems have a scientific basis.

     Spring babies are at greater risk of illnesses including schizophrenia, Alzheimer's disease, asthma

and autism.

     They may also be less clever than classmates born in other parts of the year.

1. From the passage we can know if a baby is born on February. 20, it will probably become a _____.

A. footballer      

B. doctor        

C. pianist      

D. teacher

2. According to the passage, which of the following statements is true?

A. Researchers can explain why babies will have different careers in the future

B. Researchers make the conclusion just by analyzing the birth of people in 19 separate occupations

C. Being born in a certain month will certainly determine what a baby will do in the future

D. Being born in different months has no influence on what a baby will do in the future

3. What does the underlined word "correlation" in Paragraph 5 mean?

A. close connection            

B. great influence  

C. effective solution             

D. reasonable conclusion  

4. What's the purpose of this passage?

A. To discuss a baby's birth month      

B. To describe different professions

C. to explain babies' some trends      

D. To introduce a new discovery

填空题