如图所示,一足够长的粗糙的水平传送带在电机的带动下以恒定的速度v沿顺时针方向运动

题型:不定项选择

问题:

如图所示,一足够长的粗糙的水平传送带在电机的带动下以恒定的速度v沿顺时针方向运动,其表面的动摩擦因数为μ,现从传送带左端轻放一个物体m,当物体速度刚好达到v时,又放上第二个,如此不断向右端传送物体,下列说法正确的是

[ ]

A.电机的输出功率为μmgv

B.若提高传送带的转动速率,在传送物体的过程中,电机的输出功率将提高

C.相邻两个匀速运动的物体间距离为

D.物体与传送带间由摩擦力而产生的热功率为mv2

考点:功率电功率热功率
题型:不定项选择

从Na、C、H、O四种元素中选择适当的元素按要求填空.

(1)用适当的数字和符号填空:

①两个氧分子______;②双氧水中氧元素显-1价______.

(2)写出符合下列要求的物质的化学式:

①用作焙制糕点发酵粉的是______;

②用煤炉取暧时发生中毒,主要原因是由于煤燃烧时产生的______排放不畅而引起的.

题型:不定项选择

A man once said how useless it was to put advertisements in the newspapers. "Last week," said he, "my umbrella was stolen from a London church. As it was a present, 1 spent twice its worth in advertising, but didn't get it back."

"How did you write your advertisement?" asked one of the listeners, a merchant.

"Here it is," said the man, taking out of his pocket a slip cut from a newspaper. The other man took it and read, "Lost from the City Church last Sunday evening a black silk umbrella. The gentleman who finds it will receive ten shillings on leaving it at No l0 Broad Street."

"Now," said the merchant, "I often advertise, and find that it pays me well. But the way in which an advertisement is expressed is of extreme importance. Let us try your umbrella again, and if it fails, I will buy you a new one."

The merchant then took a slip of paper out of his pocket and wrote: "If the man who was seen to take an umbrella from the City Church last Sunday evening doesn't wish to get into trouble, he will return the umbrella to No. 10 Broad Street. He is well-known."

This appeared in the paper, and on the following morning, the man was astonished when he opened the front door. In the doorway lay at least twelve umbrellas of all sizes and colors that had been thrown in and his own was among them. Many of them had notes fastened to them saying that they had been taken by mistake, and begging the loser not to say anything about the matter.

小题1: This is a story about_______.

A.how a man lost and found his umbrella

B.how to make an effective advertisement

C.how to find lost things

D.how to put an advertisement in the newspaper小题2: "If it fails, I will buy you a new one "suggested that______.

A.he was rich enough to afford an umbrella

B.he was quite sure of his success

C.he was not sure he would get the umbrella back

D.he was ready to help others小题3:The result of the first advertisement was that______.

A.the man got his umbrella back

B.the man wasted some money advertising

C.the man found his umbrella

D.someone found his umbrella小题4:According to the first advertisement, anyone who_____ would receive ten shillings.

A.left the umbrella in the City Church

B.found the umbrella at No. I 0 Broad Street

C.gave the message to the man

D.left the umbrella at No. 10 Broad Street

题型:不定项选择

双下肢肌张力增高,腱反射亢进,巴宾斯基征阳性,神经损伤位于()

A.脊髓丘脑束

B.锥体束

C.锥体外系

D.脊髓前角运动细胞

E.外周神经

题型:不定项选择

航空机票根据服务等级分为()不同舱位。

A.头等舱

B.商务舱

C.公务舱

D.经济舱

题型:不定项选择

凝汽器注水查漏后,应及时放水,防止()。

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