问题 计算题

杂技中的“顶竿”由两个演员共同表演,站在地面上的演员肩部顶住一根长竹竿,另一演员爬至竹竿项端完成各种动作后下滑。若竿上演员自竿项由静止开始下滑,滑到竿底时速度正好为零。已知竹竿底部与下面顶竿人肩部之间有一传感器,传感器显示竿上演员自竿项滑下过程中顶竿人肩部的受力情况如图所示。竿上演员质量为,长竹竿质量

(1)求竿上的人下滑过程中的最大速度

(2)请估测竹竿的长度

答案

(1)  (2)

题目分析:(1)在演员下滑的前4秒,顶竿人肩部对竿的支持力为F1=460N,竿和上面的演员总重力为500N,人匀加速下滑,加速度为a1

在演员下滑的4秒到6秒,顶竿人肩部对竿的支持力为F2=580N,竿和上面的演员总重力为500N,人匀减速下滑,加速度为a2

演员由静止下滑,下滑4s后达到最大速度,有 。

(2)在演员下滑的前4秒,可看成匀加速下滑,下滑距离为h1

在演员下滑的后2秒,可看成匀减速下滑,下滑距离为h2

竹竿的长度

阅读理解

阅读理解。

     One of the strongest arguments for the raising of the school leaving age(ROSLA)has been that it

will bring us some way nearer to"equality of opportunity".

     Many people like to think of our present system of schooling as providing plenty of steps up the

ladder of success for clever children.It would be good to think that no one who is really bright can

be missed out when the state system is obviously so complete.It is obvious, for instance, that many

children from less wealthy homes reach university or do well in other ways.

     Unfortunately we now have plenty of proofs that many children of every level of ability do much

less well than they could.For instance, during the years of national military service it was possible

to test the intelligence(智力)of all male 18 - to - 20 - year - olds. Half of those soldiers who were

placed in the two highest ability groups had left school at 15.

     It has also been shown that the percentage of working class children going to university is almost

the same now as it was in 1939.One study of 5,000 children from birth to 21 years old shows that

up to half the bright pupils from working class homes left school when they reached 16 years old.

Moreover, there is no difference in intelligence between the sexes, but far more boys than girls stay

in education after 16.

      It is clear from this and many other proofs that many children are still leaving school too early to

benefit from the prizes-money, social respectability, and interesting jobs-which higher education gives.

It is clear too that the reasons why such children leave have much to do with their social background.

Their parents often need the extra money another money-earner would bring in; they don't value

education for itself because their own was probably dull and unhappy.It is not so much that they

force their sons and daughters to leave school, rather that they tend to say, "it's up to you".

1.It is hoped that ROSLA will give all children         .

A.a more enjoyable time at school

B.the same chances in society

C.the right to a better school

D.higher scores in intelligence tests

2.People would like to think that        .

A.equal numbers of poor and wealthy children reach university

B.those with the least money get the best education

C.intelligent children are always selected by the system

D.only really clever children do well

3.Working class children are thought to be at a disadvantage because       .

A.many of the clever ones leave school early  

B.fewer go to university than ever before

C.more than half leave school when they are 16 

D.fewer boys than girls stay at school after 16

4.Many children leave school early because        .

A.their social background makes them unhappy

B.they have to give something to their family's income

C.their school is a dull and unhappy place

D.their parents don't allow them to make their own decisions

5.This article shows that equal opportunity in education        .

A.is a thing of the past

B.has not yet been achieved

C.is there for those who deserve(值得拥有)it  

D.has greatly improved our society

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