问题 多选题

细长轻绳下端栓一小球构成单摆,在悬挂点正下方

1
2
摆长处有一个能挡住摆线的钉子A,如图所示,现将单摆向左方拉开一个小角度,然后无初速度地释放,对于以后的运动,下列说法正确的是(  )

A.摆球往返运动一次的周期比无钉子时的单摆周期小

B.摆球在左、右两侧上升的最大高度一样

C.摆球在平衡位置左右两侧走过的最大弧长相等

D.摆球在平衡位置右侧的最大摆角是左侧的两倍

答案

A、摆线被钉子挡住后,绕A点做单摆运动,摆长发生变化,则周期也要发生变化.以前往返一次的周期T=2π

l
g
.挡住后,往返一次的周期为π
l
g
+π
l
2g
.故A正确.

    B、根据机械能守恒定律,摆球在左、右两侧上升的最大高度一样.故B正确.

    C、由几何关系得,右边的弧长小于左边的弧长,故C错误.

    D、由几何关系得,摆球在平衡位置右侧的最大摆角不是左侧的两倍.故D错误.

故选AB.

阅读理解

阅读理解。

     I'm confused (困惑) these days. We are taught at home and at school that using violence (暴力) is the

  least civilized (文明的) way to solve problems. For example, last week I thought about hitting my friend

 for winning a beautiful shell while we were playing at the beach. I talked with him instead and we came

 to an agreement. If two adults had a disagreement, and if they used violence towards each other in order

  to win, is it all right?

     When two countries disagree, they often fight a war. Why is using violence not okay at home, at school,

  or in your country but okay between countries? So many people have been killed because of wars, not

  only soldiers but ordinary people, even small children and babies. And refugees (难民) exist, too.

     A war is a great violence, like two people fighting over a shell, just much bigger. Adults say they are

  fighting wars in order to solve problems and make peace. But can you really "make peace" by killing so

 many people? I don't think bombs (炸弹) can reach people's hearts and change them. Bombs can't

 create love and caring, and that's what we need in the world. Why do adults use violence so quickly?

 Why can't they use their wisdom (智慧) and talk it over?

     Adults might say that things are not that easy. But they are the ones that teach us to be kind, not to hurt

  people, and not to kill. Why don't they act as what they say?

                                                                                    —A page from a 12-year-old boy, Joshua's diary.

1. At the beach, Joshua _____.

    A. hit his friend

    B. won a beautiful shell

    C. played with a beautiful shell

    D. came to an agreement with his friend

2. Joshua hates wars between countries because _____.

    A. he is afraid of wars

    B. he doesn't understand adults

    C. wars create death and refugees

    D. wars are not the only way to make peace

3. What's the key to peace in Joshua's opinion?

    A. Love and care for each other.

    B. Don't use violence so quickly.

    C. Stop using bombs in wars.

    D. Don't hurt or kill people in wars.

4. From the reading we can see Joshua wants adults to _____.

    A. learn from children

    B. be children's models

    C. be kind to children

    D. teach children how to solve problems

选择题