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 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 s 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. [简答题]人类历史上第一部药典是哪部药典?
[单选题]‘公务卡分期付款业务’是青岛农商银行根据持卡人的申请,对其已发生的消费交易提供分期偿还服务的业务,办理方便,最高可申请30万元,最快当天可用,月手续费____。
A.0.2% B.0.3% C.0.5% D.0.6% [单项选择]楼宇自动化系统不包括()。
A. 消防系统 B. 冷暖源系统 C. 保安系统 D. 光缆传输系统 [单选题]
慢性⽀⽓管炎的 X 线表现 为( ) A.肺部有块影 B.肺内有液平 C.肺⼤疱征象 D.肺纹理增粗 E.肺透亮度增加 [多选题]在以下( )区域内动火,应填用变电站一级动火工作票。
A.主控室 B.电缆沟道(竖井) C.变压器、压变、充油电缆等注油设备 D.蓄电池室(铅酸) [多选题]燃烧现象十分普遍,而任何物质燃烧过程的发生和发展必须具备的必要条件是()。 * *
A.燃烧产物 B.助燃物 C.可燃物 D.引火源 [单项选择]手火器伤后8小时清创,应
A. 初期缝合 B. 延期缝合 C. 二期缝合 D. 定位缝合 E. 不做初期缝合 [简答题]蓄电池充放电机的控制方式、运行方式、安全保护功能有哪些?
我来回答: 提交
|