问题 计算题

假定有前后两次声音传到人的耳朵里,如果这两次声音到达人耳的先后时间间隔大于(或者等于)0.1s,人耳就能把这两次声音分辨开。也就是说,如果这两次声音到达人耳的先后时间间隔小于0.1s,人耳就只能听到一次声音。

某中学8年级学生课外活动小组的同学为了体验声音在不同介质中传播速度不同的物理现象和人耳对声音的分辨时间。他们请一位甲同学在充满水的输送水的直铁管道上敲击一下,使铁管发出清脆的声音,另一乙同学在距敲击点510m的地方用耳朵贴近铁管听声。已知敲击声可分别从空气、水和铁管中传到另一同学,声音在空气中的传播速度是V= 340m/s,在水中的传播速度是V= 1500m/s,在铁管中的传播速度是V =5100m/s。请通过计算说明乙同学能听到几次声音?

答案

解:

声音在空气中的传播时间 t1=s/v1 = 510m/340m/s = 1.5s

声音在水中的传播时间 t2=s/v2 = 510m/1500m/s = 0.34s

声音在铁管中的传播时间 t3=s/v3 = 510m/5100m/s = 0.1s

声音在空气中与在水中的时间差t1-t2 =1.5 s-0.34 s = 1.16s

声音在空气中与在铁管中的时间差t1-t3=1.5 s-0.1 s = 1.4s

声音在水中与在铁管中的时间差t2-t3= 0.34s-0.1s = 0.24s

时间差都大于0.1秒,所以能听到3次声音。

阅读理解

阅读理解。

                                         The Greenest School in Britain 

     The pupils and teachers at Fairfield School think it's worth looking after the environment! This is what

they've been doing:

     Growing vegetables

      Fairfield School pupils started their own vegetable garden. Both children and teachers plant and water

the seeds (种子), then I hey pick the vegetables, which are used in school meals. Now they can all enjoy

healthy food at lunchtime. "School dinners are tastier than ever before!" says one pupil.

      Recycling

     The Fairfield pupils don't just bring their books to school-they bring their rubbish too! There are recycling

bins (回收箱) in the playground for cans, plastic bottles, batteries and paper. The teachers give a prize every

month to the pupil who's tried the hardest to recycle.

     Planting trees "This used to be one of the least beautiful areas of the city with no green areas, says the head

teacher Lynne Johnson. "Now every child has planted their own tree, which he or she looks after during the

week. They've made the view from the classroom more beautiful!

     Finding cleaner ways to get around

     Everyone walks or cycles to Fairfield School! "When the roads are busy, it's faster to ride bikes than to go

by car anyway," says one pupil. Even the teachers don't use their cars. "We won't encourage our pupils to look

after the environment if we don't do it ourselves!" says one teacher.

1. Every month the pupil who has done the best to recycle will __________ from the teachers.

2. Neither the __________ nor the __________ in Fairfield school go to school by car.

3. The pupils have made the view from the classroom more beautiful by __________.

4. From the passage we know that the teachers in this school set a good __________ to

    the pupils in protecting the environment.

5. They use the vegetables which are __________ and picked by themselves in school meals.

多项选择题