如图所示,声源S和观察者A都沿x轴正方向运动,相对于地面的速率分别为vs和v A.

题型:计算题

问题:

如图所示,声源S和观察者A都沿x轴正方向运动,相对于地面的速率分别为vsvA.空气中声音传播的速率为vp,设vs<vp,vA<vp,空气相对于地面没有流动.

(1)若声源相继发出两个声信号.时间间隔为Δt,请根据发出的这两个声信号从声源传播到观察者的过程.确定观察者接收到这两个声信号的时间间隔Δt'.

(2)请利用(1)的结果,推导此情形下观察者接收到的声波频率与声源发出的声波频率间

 
的关系式.

 

考点:多普勒效应
题型:计算题

Skiing only caught on for ordinary Chinese in the mid-1990s in the country’s north and northeast, but has since developed into a pastime that can be practiced nationwide. Here are four resorts(度假胜地) worthy of consideration.

Yabuli Ski Resort

The ski resort, built on Yabuli Sun Mountain, part of the Changbai Mountain Range, is located in China’s northernmost province, Heilongjiang.

It has the best snow quality, skiing trails and impressive views. Wild animals are often spotted on the site.

The resort serves as the primary training centre for China’s national teams. It also has a trail vertical drop from 200 meters to 1,200 meters with an average drop of 700 meters.

What’s cool: The largest ski resort in China.

Beijing Huaibei International Ski Resort

This is a great destination for snowboarders and skiers to escape the rush life of the city and is a large recreational spot that boasts excellent ski slopes, world-class facilities, beautiful natural scenery, as well as convenient accommodation and dining services.

Travelers are also able to take a bird’s eye view of the Great Wall by catching a cable car along 1,200 meters.

What’s cool: Close to the Great Wall and Beijing’s largest ski resort.

Shennongjia Ski Resort

Opened in 2004, the ski resort is located in the inland of Shennongjia. It covers an area of 100,000 square meters and is only 0.5 km from the Shennongjia National Nature Reserve.

There are ski tracks for beginners and more than 20 coaches for tourists. While experiencing the excitement of skiing, people can also admire Shennongjia’s distinctive scenery of countless different odd mountain valleys, unknown beautiful flowers and plants.

What’s cool: Largest winter sports complex for skiers from South and Central China.

Changbai Mountain Ski Resort

The ski resort is an ideal place for skiing and ice-skating because of its well-constructed ski tracks, comprehensive winter sports training facilities and breathtaking environment.

Enthusiasts can also choose other activities including motor skiing, sleigh skiing, shooting and hunting.

The area’s natural hot springs are another attraction of the resort.

What’s cool: The resort is located in the heart of Changbai Mountain Nature Reserve’s thick forest and has natural hot springs.

小题1: The passage is intended to ______.

A.encourage people to learn skiing during holidays

B.attract people to ski in these places

C.offer services of booking tickets for skiing

D.provide people with a better understanding of skiing小题2:In what way is Changbai Mountain Ski Resort different from the other three resorts?

A.It has various training facilities.

B.It has coaches for tourists.

C.It has natural hot springs.

D.It has breathtaking natural scenery.小题3:China’s national teams are usually trained at_______.

A.Yabuli Ski Resort

B.Shennongjia Ski Resort

C.Changbai Mountain Ski Resort

D.Beijing Huaibei International Ski Resort

题型:计算题

血分证的辨证要点是______,斑疹密布,舌质______。

题型:计算题

根据英国资产阶级革命的发展进程,下列事件按先后顺序排列正确的一组是

①查理一世重新召开议会 ②苏格兰人民起义 ③克伦威尔就任“护国主” ④1688年宫廷 * * [ ]

A.①②③④

B.②①③④

C.①②④③

D.②①④③

题型:计算题

《锅炉压力容器使用登记管理办法》中规定:经检验评定判废的压力容器,检验单位只向使用单位出具书面报告即可()

题型:计算题

在标定1米侧滑台滑板动作力,在侧滑量为5m/km时拉力为()

A、<40

B、<60N

C、<70N

D、<120N

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