问题 问答题

(1)图A中ABO可看成杠杆O为支点,请在图中画出该杠杆的动力臂和所受阻力的示意图.

(2)如图B所示,某人站在A处用一根绳子和两个滑轮提起物体M,画出最省力的绕线.

(3)如图C所示为利用钓鱼竿钓鱼的示意图,D为支点,F1是手对鱼竿的作用力,请画出:鱼线对钓鱼竿拉力F2的示意图和F1的力臂.

(4)根据实物连接图D,在右面的方框内画出相应的电路图.

答案

(1)在图中,动力指的是作用在杠杆上的力,过支点O作动力作用线的垂线段;过B点做竖直向下的阻力F2.如图所示:

(2)用3段绳子承担物重,绳端拉力向上.如图所示:

(3)过拉力作用点作竖直向下的拉力F2;过支点O作F1作用线的垂线段(即动力臂L1).

(4)由实物电路图可知,灯L1与L2并联,其中S1控制干路,S2控制L1所在的支路,根据实物图作出电路图,电路图如图所示:

阅读理解

阅读理解。阅读短文,从A、B、C、D中选出最佳答案。

     It is easier to go downhill than to climb uphill. So it is easier to fall into bad habits than into good ones.

     Bad habits do not come suddenly. They come little by little without one being aware of their danger.

 School boys first pick up little bad habits in school and on the street. When they can't write their lessons,

  they copy from their schoolmates. If they see bigger boys smoking, they also want to learn to smoke. If

 they see their friends gambling they want to gamble. When they get bigger, the habits become stronger and

  stronger so that they can no longer get rid of them. From copying they learn to steal, from gambling, they

 learn to cheat. At last they become suspected by everybody. How necessary it is that we get rid of the

 bad habits in the beginning!

1. It is easier to fall into ______than into________.

    A. good habits, bad habits

    B. bad habits, good ones

    C. bad habits, good one

2. Bad habits come________.

    A. suddenly  

    B. little by little

    C. faster and faster

3. Where do schoolboys pick up little bad habits first?

    A. In school

    B. On the street  

    C. in school and on the street

4. When schoolboys get bigger, their bad habits become_______.

    A. stronger and stronger

    B. weaker and weaker

    C. better and better

5. It is important for us_________.

    A. to copy with them

    B. to learn to steal and cheat

    C. to get rid of the bad habits in the beginning

选择题