问题 问答题

如图所示,两个质量各为m1和m2的小物块A和B,分别系在一条跨过定滑轮的软绳两端,已知m1>m2.现要利用此装置验证机械能守恒定律.

(1)若选定物块A从静止开始下落的过程进行测量,则需测量的物理量有______.

①物块的质量m1、m2

②物块A下落的距离及下落这段距离所用的时间;

③物块B上升的距离及上升这段距离所用的时间;

④绳子的长度.

(2)为提高实验结果的准确程度.某小组同学对此实验提出如下建议:

①绳的质量要轻;

②在“轻质绳”的前提下绳子越长越好;

③尽量保证物块沿竖直方向运动,不要摇晃;

④两个物块的质量之差要尽可能小.

以上建议中对提高准确程度确实有作用的是______.

(3)写出一条上面没有提到的对提高实验结果准确程度有益的建议:______.

答案

(1)通过连接在一起的A、B两物体验证机械能守恒定律,即验证系统的势能变化与动能变化是否相等,A、B连接在一起,A下降的距离一定等于B上升的距离;A、B的速度大小总是相等的,故不需要测量绳子的长度和B上升的距离及时间.故选①②或①③均可以.

(2)如果绳子较重,系统的重力势能就会有一部分转化为绳子的动能,造成实验误差;绳子不宜太长,长了形变对实验的影响越大;m1、m2相差越大,整体所受阻力相对于合力对运动的影响越小.物体末速度v是根据匀变速直线运动求出的,故要保证物体在竖直方向运动.这些都是减小系统误差,提高实验准确程度的做法.故选:①③

(3)实验误差来自测量:所以多次取平均值可减少测量误差,又绳子伸长量尽量小,可减少测量的高度时的误差.

故答案为:(1)①②或①③; (2)①③;(3)多次取平均值可减少测量误差或绳子伸长量尽量小等.(意思对即可)

阅读理解

The history of newspapers is an often-dramatic chapter of the human experience going back some six centuries.In Renaissance Europe handwritten newsletters circulated(发行) privately among merchants,passing along information about everything from wars and economic conditions to social customs and “human interest” features.The first printed newspaper appeared in Germany in the late 1400s in the form of news pamphlets(小册子) or broadsides.

In the English-speaking world,the earliest predecessors(前身) of the newspaper were corantos,small news pamphlets produced only when some event worthy of notice occurred.The first successively published title was The Weekly News of 1622.The first true newspaper in English was the London Gazette of 1666.  

In America the first newspaper appeared in Boston in 1690,entitled Public Occurrences.Published without official permission,it was immediately suppressed(查禁).Its publisher was arrested,and all copies were destroyed.The first successful newspaper was the Boston News-Letter,begun by postmaster John Campbell in 1704.By the eve of the Revolutionary War,some two dozen papers were issued at all the colonies.At the war’s end in 1783 there were forty-three newspapers in print. The Bill of Rights in 1791 at last guaranteed freedom of the press,and America’s newspapers began to take on a central role in national affairs.By 1814 there were 346 newspapers.

In the 1830s,advances in printing and papermaking technology led to an explosion of newspaper growth—the emergence(出现) of the “Penny Press”;it was now possible to produce a newspaper that could be sold for just a cent a copy.The cheap newspaper helped people to get more interesting reading materials easily.In 1850,there were 2526 different papers.By the 1910s,all the basic features of the modern newspaper had emerged.

小题1:Which of the following statements is TRUE according to the passage?

A.Handwritten newsletters came out publicly in Renaissance Europe.

B.The first printed newspaper was seen about six hundred years ago.

C.The first successively published newspaper in the English-speaking world was corantos.

D.In America the first newspaper was successful as soon as it appeared.小题2:What does the underlined phrase “Penny Press” in the last paragraph mean?

A.People can press pennies easily.

B.People can produce newspapers with little cost.

C.It is a penny factory.

D.The name of the press owner is Penny.小题3:What is the main reason for newspapers in the USA increasing so fast in the 1830s?

A.The pass of the Bill of Rights in 1791.

B.Newspapers began to take on a central role in national affairs.

C.Advances in printing and papermaking technology.

D.All the basic features of the modern newspaper had emerged小题4:Which of the following is NOT a newspaper?

A.Public Occurrences.

B.The Boston News-Letter.

C.The Bill of Rights.

D.The London Gazette.

判断题