问题 填空题

把一蜡块放入盛满酒精的容器中,溢出酒精的质量是4g;若把该蜡块放入盛满水的容器中,则溢出水的质量是______g.

(已知ρ=0.9×103 kg/m3,ρ酒精=0.8×103 kg/m3;容器足够大)

答案

(1)蜡的密度比酒精的密度大,在酒精中下沉,完全浸没在酒精中,排开的酒精的体积就是蜡块的体积;

所以根据ρ=

m
V
可得:

蜡块体积V=V=

m
ρ酒精
=
4g
0.8g/cm3
=5cm3

蜡块的质量mV=0.9g/cm3×5cm3=4.5g;

(2)蜡的密度比水的密度小,在水中漂浮,因此浮力等于蜡的重力,即F=G,

因此排开水的质量和蜡块的质量相等,为4.5g.

故答案为:4.5.

阅读理解

阅读理解

       Are your parents helicopters? That's a new term I read about. It describes parents who hover(原意指发飞机盘旋)  over their children. They worry about every little thing in their children's life: Are you

hungry? Are you thirsty? Do you feel cold? Do you need more books? .

       These parents love their children and want to make sure that everything in their life is perfect. Some

kids may find that annoying but others like being pampered. The pampered kids like the idea of being

waited on hand and foot. They like the idea of not having to make decisions.

       I don't think this is a good idea. I think it's important for kids to do things and make decisions by

themselves. This helps them grow up and become  responsible (负责任的 )  persons.

       How can you become responsible? It's easy: just start with little things. You can make your own

meals sometimes or help with cooking. You can also make your own bed and clean your room...

       Your parents are helicopters because they love you. So, tell them that you know it and that they

really shouldn't worry. Tell them they can land the helicopters because you are a responsible kid.

1. The parents become helicopters because _______ .        

A. they love their children too much, and hope their children's lives are perfect

B. they don't want their children to do anything except study

C. they have much free time to look after their children

D. they want to do everything for their children

2. If Mary's mother is a helicopter, what should Mary do according to the passage?        

A. Do everything without her mother's permission.

B. Argue with her mother and then say sorry to her mother.

C. Thank her mother for all that her mother has done for her.

D. Tell her mother that she understands and that her mother shouldn't worry.

3. The meaning of the underlined word is " _________" in Chinese.  

A. 关怀  

B. 歧视  

C. 娇惯  

D. 鼓励

4. How can children become responsible?         

A. Do as parents say.

B. Start with little things.

C. Let parents do everything.

D. Let others help them make decisions.

5. Which of the following is the best title?        

A. How to be perfect helicopters

B. Let your helicopters rest

C. Thanks for helicopters

D. The term of helicopters

单项选择题