问题 计算题

小明设计了一个测量物体质量的“托盘秤”,图(甲)是其原理示意图,其中托盘上放置物体,压力传感器R的电阻值会随所受压力大小发生变化,杠杆ABO可绕0点转动,电压表的量程为O~3V(可显示质量大小).已知OB:BA=1:2,电阻R0=100Ώ.压力传感器R表面能承受的最大压力为400N,压杆与压力传感器的接触面积为2cm2,压力传感器R的电阻值随所受压力变化的图像如图(乙)所示.电源电压恒定不变,秤达到最大称量时,电压表的示数也达到最大值,托盘和杠杆组件的质量忽略不计.求:

(1)该压力传感器能承受的最大压强;

(2)电源电压;

(3)当电压表的示数为1.5V时,托盘上被测物体的质量。(g=10N/kg)

答案

(1)2×106Pa  (2分)  (2)4.5V    (3分)  (3)75Kg    (3分)

题目分析:(1)最大压强:

(2)杆秤到最大称量时,电阻R0两端的电压U0=3V,

由图象可知,此时压力传感器的电阻R=50Ω,

电路中的电流

电源电压

(3)当电压表示数为1.5V时,

电路中电流

压力传感器两端的电压

压力传感器的电阻

由图象可知压力传感器受到的压力

根据杠杆平衡条件得:

所以托盘上物体的质量

点评:本题考查压强、电阻、电压、重力、质量等的计算,关键是公式及其变形的灵活运用,还要回分析电路的连接,能从题目所给信息中找到有用的数据,要学会分析图象.

单项选择题 B1型题
阅读理解

阅读理解

     Are you happy? Do you remember a time when you were happy? Are you seeking happiness today?

Many have sought a variety of sources for their feelings of happiness. Some have put their hearts and

efforts into their work. Too many have turned to drugs and alcohol. Meanwhile, untold numbers have

looked for it in the possession of expensive cars, exotic(异国的) vacation homes and other popular

"toys". Most of their efforts have a root in one common fact: people are looking for a lasting source of

happiness.

    Unfortunately, I believe that happiness escapes from many people because they misunderstand the

journey of finding it. I have heard many people say that, "I'll be happy when I get my new promotion."

Or "I'll be happy when I lose that extra 20 pounds." It is dangerous because it accepts that happiness is

a "response" to having, being or doing something.

     In life, we all experience stimulus(激励) and response. Today, some people think that an expensive

car is a stimulus, and happiness is a response; a great paying job is a stimulus, and happiness is a

response; a loving relationship is a stimulus, and happiness is a response. This belief leaves us the thinking

and feeling: I'll be happy when …

     It has been my finding that actually the opposite is true. I believe that happiness is a stimulus and a

response is what life brings to those who are truly happy. When we are happy, we tend to have more

success in our work. When we are happy, people want to be around us and enjoy loving relationships.

When we are happy, we more naturally take better care of our bodies and enjoy good health. Happiness

is not a response but a stimulus.

     Happiness is a conscious choice we make every day of our lives. For unknown reason to me, many

choose to be painful, unsuccessful and angry most of the time. Happiness is not something that happens

to us after we get something we want-we usually get things we want AFTER we choose to be happy.

1. From the second paragraph, we know too many people ______________.

  A. are not happy when they work hard

  B. are not happy when they drink or take drugs

  C. Are happy when they possess their own expensive cars

  D. all desire exotic vacation homes

2. Generally speaking, most people feel happy because ______________.

  A. they think happiness is rooted in their deep hearts

  B. they get what they want to have

  C. they get a great paying job

  D. they get an expensive car

3. Which of the following is right according to the author?

  A. If you want to get what you want, you first choose to be happy.

  B. We should try to get more and then we'll be happy.

  C. Most people today are happy.

  D. Work is a necessary part in our daily life

4. From the viewpoint of the author, happiness is _______________.

A. based on our needs          

B. unconditional

C. out of reach                

D. limited