问题 问答题

(1)物块沿斜面下滑的加速度大小;

(2)物块与斜面间摩擦力的大小;

(3)地面对木楔的摩擦力的大小和方向.

答案

(1)0.7m/s2 (2)4.3N  (3)0.61N  方向水平向左

(1)(5分)由匀加速运动的公式v2=v02+2ax,得

物块沿斜面下滑的加速度为m/s2=0.7m/s2 

 (2)(5分)由于a<gsinθ=5m/s2,可知物块受到摩擦力作用。分析物块受力,它受三个力,如图所示。对物块应用牛顿运动定律,有

 沿斜面方向          mgsinθ-f1=ma   

解得 N=4.3N

(3)(5分)物块垂直于斜面方向  mgcosθN1="0   "

 分析木楔受力,它受五个力作用,如图。对木楔应用牛顿运动定律,有

 水平方向  f2+f1cosθN1sinθ="0    "

 解得地面作用于木楔的摩擦力

   f2=N1sinθf1cosθ=mgcosθsinθ-(mgsinθma)cosθ

= macosθ=N=NN

 方向水平向左(与图中所设的一致,由C指向B的方向)

阅读理解

阅读理解。

     Popular music in America is what every student likes. Students carry small radios with earphones

and listen to music before class, after class and at lunch. Students with cars buy large speakers and

play the music loudly as they drive in the street.

     Adult drivers listen to music on the car radio as they drive to work. They also listen to the news

about sports, the weather and the life of American people. Most of the radio programs are music.

Pop or popular music singers make much money. They make a CD or tape and radio stations use

them in many places. Once the popular singer is heard all over the country, young people will buy

his or her tape. Some of the money from these tapes comes to the singer. Wherever the singer goes,

all the young people want to meet him or her. Now the singer has become a national star. There are

other kinds of music that are important to Americans. One is called folk music. It tells stories about

the common (普通的) life of Americans. Another is called western or country music. It is about

country life and the love between a country boy and his girl friend. They are very popular among

young people.

1. How many kinds of music are mentioned in this passage?

A. One.

B. Two.

C. Three.

D. Four.

2. The students often take radios to______.

A. study English

B. listen to news and weather report

C. enjoy music

D. play music loudly in the street

3. The pop singers can make much money because______.

A. they make CDs or tapes

B. many young people buy their tapes

C. they are national stars

D. all the people want to meet them

4. From the passage we know that folk music is about ______.

A. love stories between boys and girls

B. the common life of American people

C. Americans' country life

D. the life of singers

5. The best title for this passage should be "______".

A. Everyone likes music in America

B. Pop music in America

C. Music in America

D. Music is important to Americans

问答题 简答题