问题 选择题

如图所示,A、B为咬合传动的两齿轮,RA=2RB,则A、B两轮边缘上两点的

A.角速度之比为2:1             B.周期之比为1:2 

C.向心加速度之比为1:2         D.转速之比为2:1

答案

答案:C

本题考查圆周运动角速度线速度关系问题,A、B为咬合传动的两齿轮,RA=2RB,则A、B两轮边缘上两点的线速度相等,周期之比为2:1;向心加速度之比为1:2;转速之比为1:2;故只有C正确;

阅读理解

阅读理解。

                                                    Edison-style light bulb and CFLs

1. About 130 years ago, Thomas Edison of the USA invented the light bulb. Edison's bulb has turned night

    into day ever since. But today, many want to turn the light off.

2. The European Union recently decided that by 2009, people should stop using the Edison-style light bulb.

     Instead, they should use compact fluorescent lamps (CFLs节能灯).

3. "CFLs save energy and last longer. They can save money in the long run," said a British official. CFLs

     use 67 percent less electricity than the older bulbs. They last up to times longer. Scientists say that if

     everyone used CFLs, electrify use would be cut 18 percent. There would also be much smaller amounts

     of greenhouse gases given off.

4. But it's difficult to make people change their lighting habits. First the CFLs are more expensive. They cost

    eight times the price of the older bulbs. Many people don't like the CFL bulbs. They find it too bright. You

    cannot change the light of a CFL, either.

5. CFLs have been around for several years. However, the older lights still make up about two-thirds of total

    light bulb sales.

A. When to stop to use CFLs

B. Edison made the world bright

C. The older style lights are still used widely

D. The advantages of using CFLs

E. The disadvantages of using CFLs.

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