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【简答题】
一台四速笼型异步电动机的4个同步转速为：n s1 =3000r/min，n s2 =1500r/min，n s3 =1000r/min，n s4 =500r/min。试计算在下列两种空载分级起动的情况下，起动到最大转速时电动机的能量损耗： (1)两级起动：先由n=0到n s2 =1500r/min，而后到n s1 =3000r/min； (2)三级起动：先由n=0到n s3 =1000r/min，而后到n s2 =1500r/min，最后到n s1 =3000r/min。(假定拖动系统的转动惯量J=0.98kg·m 2 ， 定子铁耗与机械损耗可以忽略)。
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【判断题】Heracles (Hercules) was the son of Zeus and Alcmene, who was granddaughter of Perseus and wife of Amphitryon.
A.
正确
B.
错误
【单选题】Heracles and his twelve laborWhen Hercules grew up and had become a great warrior, he married Megara. They had two children. Hercules and Megara were very happy, but life didn't turn out for them the ...
A.
Eurystheus had a reputation for being mean.
B.
Hercules knew that the king would give him a tough time
C.
The hero had to serve Eurystheus for twelve years.
D.
When the tasks were completed, Hercules would become immortal.
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