问题 问答题

某同学用如图所示的装置“验证动量守恒定律”,其操作步骤如下:

A.将操作台调为水平;

B.用天平测出滑块A、B的质量mA、mB

C.用细线将滑块A、B连接,滑块A、B紧靠在操作台边缘,使A、B间的弹簧处于压缩状态;

D.剪断细线,滑块A、B均做平抛运动,记录A、B滑块的落地点M、N;

E.用刻度尺测出M、N距操作台边缘的水平距离x1、x2

F.用刻度尺测出操作台面距地面的高度h.

(1)上述步骤中,多余的步骤是______.

(2)如果动量守恒,须满足的关系是______(用测量量表示).

答案

取小球A的初速度方向为正方向,两小球质量和平抛初速度分别为mA、mA,v1、v2,平抛运动的水平位移分别为x1、x2,平抛运动的时间为t.

        需要验证的方程:0=mAv1-mBv2

                 又v1=

x1
t
v2=
x2
t

代入得到mAx1=mBx2

故不需要用刻度尺测出操作台面距地面的高度h.所以多余的步骤是F;

故答案为:F,mAx1=mBx2

填空题

阅读理解。

    We know the mosquito (蚊子) very well. Mosquitoes fly everywhere. They can be found almost all

over the world, and there are more than 2,500 kinds of them.    

     No one likes the mosquito. But the mosquito may decide that she loves you. She? Yes, she. It's true

that the male mosquito doesn't bite (咬) and only the female mosquito bites because she needs blood to

lay eggs. She is always looking for things or people she wants to bite. If she likes what she finds, she

bites. But if she doesn't like your blood, she will turn to someone else for more delicious blood. Next

time a mosquito bites you, just remember you are chosen. You're different from the other people!    

     If the mosquito likes you, she lands on your body without letting you know. She bites you so quickly

and quietly that you may not feel anything different. After she bites, you will have an itch on your body

because she puts something from her mouth together with your blood. By the time the itching begins, she

has flown away.  

     And then what happens? Well, after her delicious dinner, the mosquito feels tired. She just wants to

find a place to have a good rest. There, on a leaf or a wall, she begins to lay eggs, hundreds of eggs.

1. "itch" means ______ in Chinese.

A. 叫声  

B. 麻木  

C. 剧痛  

D. 痒

2. How many kinds of mosquitoes are there in the world?             

A. There are 2,500 kinds of them.    

B. There are more than 2,500 kinds of them.    

C. There are many kinds of them.    

D. There are less than 2,500 kinds of them.

3. "But the mosquito may decide that she loves you." "she" refers  to (指的是) ______.

A. the male mosquito         

B. the young mosquito    

C. the old mosquito          

D. the female mosquito

4. The mosquito is always looking for ______.   

A. people she dislikes    

B. things or people she doesn't want to bite    

C. things or people she wants to bite    

D. animals she doesn't want to bite

5. Which of the following sentences is true?  

A. The itching begins before the mosquito bites you.    

B. Mosquitoes need blood to lay eggs.    

C. You feel terrible when the mosquito bites you.    

D. All the mosquitoes like to bite people for blood.

填空题