问题 问答题

小军想设计一个实验证明液体产生的压强一定时,压力跟受力面积成正比.实验桌上有粗细不等的平底试管六只(直径已知)、装有适量水的水槽一个、天平一架、配套砝码一盒,足量细沙、小勺一把、面巾纸一盒.

(1)写出主要的实验步骤

(2)画出实验数据记录表.

答案

答:(1)①用D表示试管的直径.将其记录在表格中;

②取一个试管,在试管中装入适量细沙,使其竖直漂浮在水槽中.用刻度尺测出试管浸入水槽的深度用h表示,将试管从水槽中取出擦净,用天平称其总质量用m表示.并将m、h的数据记录在表格中;

③取不同的试管,仿照步骤②再做5次实验,调节细沙量,使每次试管浸入水槽的深度均为h,用天平称出各次试管和沙的总质量m.并将各次的m、h的数据记录在表格中; 

④根据公式 S=

1
4
πD2、F=mg 计算出试管底面积和各次的压力并记录在表格中.

(2)根据分析,表格中应有直径、底面积、质量、试管在水中的深度、压力各项,见下表:

D/m
S/m2
m/kg
h/m
F/N

单项选择题
阅读理解

阅读理解。

     In many countries the standard of living enjoyed by their people has increased rapidly in recent years.

Sadly, not everyone in these countries is so fortunate and many people in rich countries are homeless.

     The reasons for homelessness are various, but poverty (贫穷) is undoubtedly one of the main causes.

The homeless people may have become jobless and then been unable to pay their rent and so no longer

have a roof over their heads. Often, the fact that unemployed people get help from the government prevents

this from happening, but not always.

     Some homeless people are mentally ill and have no one to look after them. Some are young people who,

for one reason or another, have left home and have nowhere to live. Many of them have had a serious

disagreement with their parents and have left home, choosing to go to a city and live on the streets. Sometimes

they have taken such action because they have been unable to get on with a step-parent.

     Many homeless people get into the habit of begging to get enough money to stay alive, but many of the

general public refuse to give anything to beggars. Often they are moved on by the police, being accused (指

控), whether rightly or wrongly, of forceful begging. There are many who disrespect homeless people.

     Some cynics (愤世嫉俗的人) declare that homeless people choose to live the life which they lead. But

who would willingly choose to live in z shop doorway, under a bridge or in a cardboard box?

1. According to the text, what causes some people to be homeless?

A. Lack of money.

B. The increased standard of living.

C. No government help.

D. Agreement with their parents.

2. It can be inferred from the text that _____.

A. the homeless are willing to live under a bridge or in a cardboard box

B. you will not find homeless people in countries with a high standard of living

C. the mentally ill live on the stress because they want the company of other homeless people

D. the unemployed who receive help may still be among the homeless

3. In paragraph 2, "a roof over their needs" most probably means _____.

A. a cap

B. a car

C. a home

D. a covering

4. The author thinks that the homeless people are _____.

A. pitiful

B. troublesome

C. respectable

D. admirable