问题 选择题

如图为甲、乙两等质量的质点作简谐运动的图象,以下说法中正确的是(  )

A.甲、乙的振幅各为20cm和1cm

B.甲比乙振动得慢

C.0~2s内,甲、乙的加速度均为负值

D.t=4s时,甲的速度和乙的加速度都达到各自的最大值

答案

A、由图甲的振幅A=2cm,乙的振幅A乙=1cm.故A错误.

    B、甲的周期T=4s,乙的周期T=8s,则甲振动快.故B错误

    C、简谐运动的加速度方向总是与位移方向相反,0~2s内,甲、乙位移均为正值,则加速度均为负值.故C正确.

    D、t=4s时,甲、乙都经过平衡位置,速度最大,加速度最小.故D错误.

故选C

阅读理解

阅读理解。

     Many adults think that the decision to buy a computer is theirs. They are the world's webmasters.

But now, a US survey (调查) has found children are getting more and more interested in the Internet.

The number of children using the Internet has grown to three times in the past three years.

     Three years ago, the number of two to seventeen years old children entering the web world was

eight million. Today, the number has increased to 25 million. By the end of the year 2005, the number

of children on-line is expected to be 42 million.

     More and more children are using the net because their parents use it.

      The survey showed that the number of parents using the net has changed from 4.5 million and

16.4 million. The survey found many other interesting facts.

     Almost two-thirds of US families have home computers. Forty-six percent of all family members

are hooked (沉迷于) on the Internet.

      Girls are using the net as much as boys.

     In five years, schools will become the main gateways to the Internet for children.

1.By the end of year 2005, the number of children on-line will be _____ more than today.[ ]

A. 8 million

B. 17 million

C. 25 million

D. 42 million.

2. Why are more and more children using the net now? [ ]

A. Because they needn't go to school any more.

B. Because they will have exams on the net.

C. Because their parents often use the net and that affects (影响) them.

D. Because their teachers give lessons on the net all day.

3. What do you think of girls going on-line? [ ]

A. The girls go on-line less than boys.

B. They spend a lot of time on the net like boys.

C. They are weak in using the net.

D. The girls only use the net at school.

4.What may be the best title of the passage? [ ]

A. Adults Become the Owners of the Internet.

B. Children Lead the Internet.

C. How Do Children Use the Net?

D. The Growing Number of People Entering the Web World.

5. What are other interesting facts found by the survey?

(1) More and more children are interested in the Internet.

(2) Almost two-thirds of US family have home computers.

(3) Forty-six percent of all family members are hooked on the Internet.

(4) Boys use the net as much as girls.

(5) Schools will become the main gateways to the Internet for children in five years.[ ]

A. (1)(2)(3)(4)

B. (1)(2)(4)(5)

C. (2)(3)(4)(5)

D. (1)(3)(4)(5)

多项选择题