问题 问答题

小明用如图所示的装置探究小车沿斜面下滑时速度的变化.

(1)小明在斜面中点处放一金属片,用停表记下小车从斜面顶端滑下至撞击金属片的时间t1,并用刻度尺量出小车通过的距离 s1

(2)小明把金属片放在斜面终点,在斜面中点位置释放小车,测出小车下滑到底端撞击金属片的时间t2和这段时间内小车通过的距离s2

(3)用测得的数据求出各段的平均速度.小明发现v1=v2,于是得出结论:小车从斜面顶端滑至底端做匀速直线运动.

你认为小明的实验过程妥当吗?______;为什么?______.

答案

实验过程中,小明让小车从斜面中点滑到底端,这与小车从顶端滑到中点的运动过程相同,不能探究小车下滑时速度的变化,小明的做法不妥.正确的做法是:先让小车从顶端滑到中点,测出小车的路程与运动时间,然后让小车从顶端滑到底端,测出小车的路程与运动时间,然后求出两个过程的平均速度,进行比较,得出结论.

故答案为:不妥当;小车从斜面中点滑到底端,与小车从顶端滑到中点的运动过程相同,不能探究小车下滑时速度的变化.

选择题
阅读理解

Yousuf Karsh,the Canadian portrait artist who photographed many of the most influential figures of the 20th century,died in a Boston hospital on July l3 th,2002.He was 93.

Working from a studio in Ottawa,Karsh produced famous portraits of such subjects as Winston Churchill,John F.Kennedy,Ernest Hemingway and Albert Einstein.Actually he has become almost as famous as his legendary subjects.In the latest edition of Who’s Who,which listed the most notable people of the last century,Karsh was the only Canadian of the 100 famous people listed——51 0f whom Karsh had photographed.

As a master portraitist,often working in black and white.Karsh was famous for talking to his subjects as he was getting the shot’s composition just right,asking them questions and putting them at ease.In preparation,he read as much as he could about the sitters,but avoided having the idea beforehand of how he would photograph them.He sought, as he wrote in Karsh Portfolio in 1967,to capture the “essential element which has made them great,” explaining,“All I know is that within every mall a secret is hidden,and as a photographer, it is my task to reveal it if I can.”

Karsh was born in America in 1908,and his uncle,George Nakash,brought him to John Garo,all outstanding photographer,to teach him in 1928.Four years later,Karsh set up his own studio in Ottawa.

In December of 1941,his memorable portrait of Winston Churchill brought Karsh into international fame.Canada’s Prime Minister Mackenzie King arranged for him to photograph Churchill following Churchill’s speech in the House of Commons.Not told,Churchill lit up a cigar, “Why was I not told of this?’’ Karsh asked him to remove the cigar and,when he didn’t,stepped forward and gently removed it with the comment,“Forgive me,Sir.”Churchill glowered (怒目而视) as the shot was taken,then permitted Karsh to take still another,;jokingly commenting,“You can even make a roaring lion stand still to be photographed.” The Churchill portrait has since appeared in publications all over the world.

Karsh traveled to London in 1943 with his portable studio —— an 8-by-10 view camera and many studio lamps to photograph such notables as George Bernard Shaw and the royal family.All these portraits fully illustrate Karsh’s ability.

小题1:What did Karsh seek to do most in working?

A.Capture the essence and greatness of the character.

B.Present the true and vivid expression of the subject.

C.Make the photograph more colorful and expressive.

D.Reveal the idea he has got in preparing for the shot.小题2:The underlined word “sitters”in Para 3 probably means __________ .

A.characters seated

B.subjects questioned

C.models photographed

D.photographs taken小题3:The last three paragraphs are mainly developed by __________ .

A.following time order

B.providing examples

C.making comparisons

D.giving causes and effects小题4:From the passage,we can learn that __________ .

A.Churchill was asked to stand still when Karsh took a photograph of him

B.Churchill’s portrait hanging in the House of Commons gave Karsh great fame

C.Karsh was listed as one of the 100 notables by Who’s Who in the last century

D.Karsh could skilfully adjust the subjects’ mood when photographing them