问题 问答题

(1)升降机匀速上升;

(2)升降机以4 m/s2的加速度匀加速上升;

(3)升降机以5 m/s2的加速度匀加速下降。

答案

(1)600N  (2) 840N   (3) 300 N

人站在升降机中的体重计上受力情况.

(1)当升降机匀速上升时由牛顿第二定律得

F=FN-G=0

所以,人受到的支持力FN=G=mg=60×10N=600N.根据牛顿第三定律,人对体重计的压力即体重计的示数为600N.

(2)当升降机以4 m/s2的加速度加速上升时,根据牛顿第二定律FNG=maFN=Gma=mga)=60×(10+4)N=840N,此时体重计的示数为840N,大于人的重力600 N,人处于超重状态.

(3)当升降机以5 m/s2的加速度加速下降时,根据牛顿第二定律可得mgFN=ma

N="300" N,体重计的示数为300 N,小于人本身的重力,人处于失重状态.

阅读理解

LONDON (Reuters) — British milkman Steve Leech, who saved several shops and flats by putting out a fire with 320 pints of milk, was celebrating Thursday after winning a national bravery award.

Leech, 35, named “Hero Milkman” by the National Dairymen’s Association, said that he had noticed smoke coming out of a shop in Cornwall, southern England, while delivering (递送) milk as usual a year ago.

“I saw the flats up above and thought I’d better do something. So I kicked the door in and started pouring milk everywhere,” Lee told Reuters Thursday.

“When firemen arrived, the fire was almost out,” he said. Firemen said he had helped save the lives of eight people living in the flats above the shops.

It was hard work opening all those bottles, especially since they have tamper-proof lids. But it was even harder trying to explain to my boss where all the milk had gone.”

小题1: This is a(n) _______ from London.

A.poster

B.review

C.advertisement

D.news report小题2: Leech was awarded the prize for his _______.

A.hard work

B.brave behaviour

C.invention

D.patriotic behaviour小题3: Which is the correct order of what Leech did about a year ago?

①The fire was almost put out.              ②He kicked the door in.

③He noticed smoke coming out of a shop. ④He delivered mile as usual.

⑤He poured milk everywhere.

A.①②③④⑤

B.④②③⑤①

C.③④①②⑤

D.④③②⑤①小题4:The underlined sentence in the last paragraph suggests (暗示) that tamper-proof lids add to the difficulty of _______ those bottles.

A.stealing

B.breaking

C.opening

D.wasting小题5: Which is NOT TRUE according to the passage?

A.Leech put out a fire with milk at the age of 34.

B.Cornwall is in the north of England.

C.Leech saved eight people in the shops.

D.The fire was already out before firemen arrived.

多项选择题