问题 选择题

如图所示装置,两物体质量分别为m1、m2,悬点a和b之间的距离大于滑轮直径的2倍,不计一切摩擦,若装置处于静止状态,则:   

A.m1大于m2

B.m2大于m1/2 ;

C.m2可能等于m1/2;

D.θ1等于θ2

答案

BD

题目分析:以左边滑轮为研究对象,绳子的拉力相等,根据对称性可知角度,绳子的拉力的合力等于m1g,由平行四边形可知绳子的拉力组成的平行四边形为菱形,对角线为m1g,由于斜边大于直角边可知m2大于m1/2,B对;m1和m2大小无法比较,AC错

点评:本题难度中等,注意研究对象的选取,利用平行四边形求解力的合力,巧妙应用对称性也是常用的判断手段

填空题
阅读理解

阅读理解

     Imagine you're at a party full of strangers. You're nervous. Who are these people? How do you

start a conversation? Fortunately, you've got a thing that sends out energy at tiny chips in everyone's

name tag (标签). The chips send back name, job, hobbies, and the time available for meeting-whatever. Making new friends becomes simple.

     This hasn't quite happened in real life. But the world is already experiencing a revolution using RFID

technology.

     An RFID tag with a tiny chip can be fixed in a product, under your pet's skin, even under your own

skin. Passive RFID tags have no energy source - batteries because they do not need it. The energy

comes from the reader, a scanning device (装置), that sends out energy (for example, radio waves) that

starts up the tag immediately.

     Such a tag carries information specific to that object, and the data can be updated. Already, RFID

technology is used for recognizing each car or truck on the road and it might appear in your passport.

Doctors can put a tiny chip under the skin that will help locate and obtain a patient's medical records.

At a nightclub in Paris or in New York the same chip gets you into the VIP (very important person)

section and pays for the bill with the wave of an arm.

     Take a step back: 10 or 12 years ago, you would have heard about the coming age of computing.

One example always seemed to surface: Your refrigerator would know when you needed to buy more

milk. The concept was that computer chips could be put everywhere and send information in a smart

network that would make ordinary life simpler.

      RFID tags are a small part of this phenomenon. "The world is going to be a loosely coupled set of

individual small devices, connected wirelessly,"predicts Dr. J. Reich. Human right supporters are nervous

about the possibilities of such technology. It goes too far tracking school kids through RFID tags, they

say. We imagine a world in which a beer company could find out not only when you bought a beer but

also when you drank it. And how many beers. Accompanied by how many biscuits.

     When Marconi invented radio, he thought it would be used for ship-to-shore communication, not for

pop music. Who knows how RFID and related technologies will be used in the future. Here's a wild

guess: Not for buying milk.

1. We know from the passage that with the help of RFID tags, people _______.

A. will have no trouble getting data about others

B. will have more energy for conversation

C. will have more time to make friends

D. will not feel shy at parties any longer

2. Passive RFID tags chiefly consist of _______.

A. scanning devices    

B. radio waves    

C. batteries    

D. chips

3. Why are some people worried about RFID technology?

A. Because children will be tracked by strangers.

B. Because market competition will become more fierce.

C. Because their private lives will be greatly affected.

D. Because customers will be forced to buy more products.

4. The last paragraph implies that RFID technology _______.

A. will not be used for such matters as buying milk

B. will be widely used, including for buying milk

C. will probably not be used for pop music

D. will be limited to communication uses