问题 问答题

从离水平地面高为HA点以速度v0斜向上抛出一个质量为m的石块,已知v0与水平方向的夹角为θ,不计空气阻力,求:

(1)石块所能达到的最大高度;

(2)石块落地时的速度.

答案

(1)石块所能达到的(距地面)最大高度为:.

(2)石块落地时的速度大小为:.

本题考查学生对机械能守恒定律内容的理解能力,以及灵活选择机械能守恒定律表达形式处理问题的能力.

石块抛出后在空中运动过程中,只受重力作用,机械能守恒,作出石块的运动示意图如图7-7-3.

图7-7-3

(1)设石块在运动的最高点B处与抛出点A的竖直高度差为h,水平速度为vB,则vB=v0x=v0cosθ

石块从AB,根据机械能守恒定律,ΔEk减=ΔEp增,

①②式联立得

则石块所能达到的(距地面)最大高度为:.

(2)取地面为参考平面,对石块从抛出点A至落地点C的整个运动过程应用机械能守恒定律,

E2=E1

解得石块落地时的速度大小为:.

阅读理解

B

For a 400-year-old art form, operas had a bad fame: overweight actresses singing the words which are hard to understand in one of those romance languages you were supposed to learn in high school. And with tickets costing as much as $ 145 a performance, opera goers also have a certain appearance in people’s mind: rich, well-dressed and old.

But now opera companies around the country are loosening their ties and kicking off their shoes in an attempt to bring the opera to the audience. It needs to keep it alive, the young and not-so-rich.

Opera producers have found that to attract this crowd, they need to make the opera closer to common people. That means no formal suits, old-styled theatre or band-breaking ticket prices. And because young people don’t or won’t come to the opera, companies are bringing the opera to them, giving performances in such unusual places as parks, libraries and public schools.

The Houston Grand Opera’s choice is the public library, where it performs “mobile operas”, shortened versions (剧本) of child-friendly operas. This summer’s production is Hansel & Gretel. By performing smaller versions of large productions, producers are able to make people interested while keeping costs at a reasonable level. The San Francisco Opera, which will be celebrating its 75th anniversary this year, is staging Cinderella free of charge, keeping costs down by employing students from its Young Artists’ Training Program.   

45.Which is the main idea of this passage?

A.Opera is famous for its long history.                                  

B.Opera is only performed for rich people.

C.Young people are not interested in opera.                              

D.Opera companies are trying to keep opera alive.

46.The underlined phrase “loosening their ties and kicking off their shoes” (paragraph 2) means ______.

A.breaking up the old rules                      B.changing the formal suits

C.making the audience at ease                  D.advertising themselves

47.The San Francisco Opera Company employs student actors in order to ______.

A.celebrate its 75th anniversary                B.reduce the cost

C.attract young people                             D.make Cinderella popular

48.From the passage we can infer that ______.

A.the tickets for operas are very expensive                               

B.operas are performed in a difficult language

C.operas are not so popular an art form today                           

D.students enjoy performing operas very much

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