首页
登录
职称英语
The prefix Mach is used to describe supersonic speed. It was named for Ernst
The prefix Mach is used to describe supersonic speed. It was named for Ernst
游客
2023-11-04
7
管理
问题
The prefix Mach is used to describe supersonic speed. It was named for Ernst Mach (1838—1916), a Czech-born Austrian physicist, who contributed to the study of sound. When twice the speed of sound, it is Mach 2. When it is near but below the speed of sound, its speed can be designated at less than Mach 1, for example, Mach 0. 90. Mach is defined as "the ratio of the velocity of a rocket or a jet to the velocity of sound in the medium being considered".
When a plane passes the sound barrier — flying faster than sound travels, listeners in the area hear thunderclaps, but the pilot of the plane does not hear them.
Sound is produced by vibrations of an object and is transmitted by alternate increase and decrease in pressure that radiate outward through a material media of molecules — somewhat like waves spreading out on a pond after a rock has been tossed into it.
The frequency of sound is determined by the number of times the vibrating waves undulate per second and is measured in cycles per second. The slower the cycle of waves, the lower the frequency. As frequencies increase, the sound is higher in pitch.
Sound is audible to human beings only if the frequency falls within a certain range. The human ear is usually not sensitive to frequencies of fewer than 20 vibrations per second, or more than about 20, 000 vibrations per second — although this range varies among individuals. Anything at a pitch higher than the human ear can hear is termed ultrasonic.
Intensity, or loudness, is the strength of the pressure of these radiating waves and is measured in decibels. The human ear responds to intensity in a range from zero to 120 decibels. Any sound with pressure over 120 decibels is painful to the human ear.
The speed of sound is generally placed at 1, 088 feet per second at sea level at 32 degrees Fahrenheit. It varies in other temperatures and in different media. Sound travels faster in water than in air, and even faster in iron and steel. It travels a mile in 5 seconds in air, it does a mile under water in 1 second, and it travels through iron in 1 /3 second. It travels through ice cold vapor at approximately 4, 708 feet per second; ice-cold water, 4,938; granite, 12,960; hardwood, 12,620; brick, 11,960, glass, 16,410 to 19,690; silver, 8,658; gold, 5,717. [br] According to this passage, "Mach" refers to
选项
A、the ratio of the air speed of an aircraft to the speed of sound.
B、a machine.
C、a Czech-born Australian physicist.
D、the pilot of the plane.
答案
A
解析
第一段提到了Mach的相关信息,其中最后一句提到,马赫(Mach)是火箭或飞机在空中的速度与声速的比率,由此可知答案为[A]。
转载请注明原文地址:https://www.tihaiku.com/zcyy/3157122.html
相关试题推荐
TheprefixMachisusedtodescribesupersonicspeed.ItwasnamedforErnst
TheprefixMachisusedtodescribesupersonicspeed.ItwasnamedforErnst
Chinesepeopleareusuallydescribedashospitable,generousandamiable.Theun
Whichstatementbestdescribestheman?[br][originaltext]M:Hi,honey!What’s
Whichstatementbestdescribestheman?[originaltext]M:Hi,honey!What’sgoing
[A]community[B]compassion[C]describe[D]distractedly[E]documenting[F]drastic[G]i
[A]community[B]compassion[C]describe[D]distractedly[E]documenting[F]drastic[G]i
[A]community[B]compassion[C]describe[D]distractedly[E]documenting[F]drastic[G]i
[A]community[B]compassion[C]describe[D]distractedly[E]documenting[F]drastic[G]i
Chinesepeopleareusuallydescribedashospitable,generousandamiable.Theun
随机试题
[originaltext]M:Didyoutakethesepictures?They’reverygood.W:Yes,Ithin
[originaltext]Americansthinkagreatdealabouttime.Theyconstantlyrefe
监理规划用于指导项目监理机构实施工程监理工作,主要内容有()。A.明确项目监
下列哪项不是虚证的临床表现A二便失禁 B自汗盗汗 C面容憔悴 D疼痛隐隐
一足月新生儿,出生体重2800g,身长48cm,面色红润,哭声响亮,吸吮有力,母
机电工程项目施工技术资料与竣工档案的特征是()。A、真实性 B、有效性 C、
CSF中葡萄糖含量A.与血糖含量相同 B.比血糖含量高1/2 C.比血糖含量
隔离开关转动机构卡阻无法转动,定性为危急缺陷
简述现代企业人力资源管理各个历史发展阶段的特点。
银行承兑汇票的承兑银行,应当按照票面金额向出票人收取()的手续费。A:千分之一
最新回复
(
0
)