问题 问答题

(1)滑板匀速直线运动的速度V1;滑板与水面的夹角为q1的大小。

(2)在运动过程中运动员可以通过调节滑板与水面的夹角来改变速度,当滑板与水面的夹角为q2=30°时,水平牵引力F2=810N,运动员在竖直方向仍处平衡,滑板此时的速率V2为多少?此时滑板的加速度a为多少?

(3)若运动员要做离开水面的空中特技动作,运动员可以先下蹬,使重心下降,使牵引力与水面的夹角a=15°斜向上。滑板与水面的夹角为q3=53°。速度为V3="5m/s," 则在离水面前(水对滑板的作用力FN还存在)牵引力F3大小至少为多少?(sin15°=0.26)

答案

(1) 5 m/s q1=37° (2) 1.74m/s2 (3) 1038N

阅读理解

Watch out, Yahoo. There is a search engine out there with super speed and accuracy. It’s very cool.

Google is the Web’s largest search engine. In just two years it has gained a reputation for surprising speed and accuracy, delivering what you are looking for in a second. The site now does this 40 million times a day --- a number achieved without spending a penny on a TV or newspaper ad.

Google doesn’t need them. In the past six months alone, the site has won a Webby (the online version of the Oscar) for technical excellence, set a new record for search engines by indexing a billion Web pages.

Yahoo still has ten times the audience, but Google consistently ranks first in customer satisfaction: 97% of users find what they are looking for most or all of the time. “You see people smile when they use it, like they’ve found something no one else knows about,” says Danny Sullivan, editor of an online newsletter.

No one is smiling more than Larry Page, 27, and Sergey Brin, 26, who seem certain to become billionaires when the company goes public, probably sometime in 2004. they make a great comedy duo(成对的表演者)。When they first met as Ph. D. students, the pair say, they found each other horrible – “I still find him horrible,” adds Brin – but driven together by a computer-science project aimed at coming up with better ways of searching the Web.

The idea behind the Google is that traditional search engines are stupid. They think relevance (关联) is based on repetition; if you type in a request for Tiger Woods, say, you’ll get websites listed according to how many times those words appear. Not only is this no guarantee of quality, but it’s also open to abuse. If you own a Tiger fan site and want to lead more people to it, simply type his name thousands of times in the site’s source code(编码).

1What does the underlined word “them” in the third paragraph refer to?

A. 40 million times              B. Speed and accuracy. 

C. TV and newspaper ads.        D. Web pages

2. Which of the following win greater customer satisfaction?

A. Yahoo        B. Tiger Woods      C. Larry Page     D. Google

3. It can be inferred that Page and Brin ______________.

A. hold very important positions in Google

B. are two ordinary computer programmers of Google.

C. used to hate each other very much

D. hold quite different opinions of computer-science

4. We can learn from the last paragraph that ___________.

A. Google is open to abuse

B. Google remains a traditional search engine

C. Google thinks relevance is based on repetition

D Google is better than traditional search engines

多项选择题