问题 计算题

如图所示,在海滨游乐场里有一种滑沙游戏,人坐在滑板上从倾角θ=37°的斜坡上由静止开始下滑,经过斜坡底端沿水平滑道再滑行一段距离停下。已知滑板与斜面和水平滑道间的动摩擦因数均为μ=0.3。若某人和滑板的总质量m=60kg,滑行过程中空气阻力忽略不计,重力加速度g取10m/s2。(sin37°=0.6   cos37°=0.8)

(1)求人从斜坡滑下时加速度的大小;

(2)若人坐着滑板从距地面高6.0m处由静止下滑,求到达斜坡底端时的速度大小。

答案

解:(1)人在斜面上受力如图所示,设人在斜坡上滑下的加速度为a,由牛顿第二定律有

联立解得a1=g(sinθ-μcosθ),代入数据得a1=3.6m/s2  

(2)

  

单项选择题
阅读理解

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, I 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.10 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 for your umbrella again, and if it </PGN0332.TXT/PGN>fails, I'll 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 colours that had been thrown, 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:The result of the first advertisement was that ______________.

A.the umbrella was found somewhere near the church

B.the man got his umbrella back

C.the man wasted some money advertising

D.nobody found the missing umbrella小题2:The merchant suggested that the man should _______________.

A.buy a new umbrella

B.write another and better advertisement

C.go on looking for his umbrella

D.report the police小题3:“If it fails, I’ll buy you a new one,” suggested that the merchant

_______________.

A.wanted to buy him a new umbrella

B.didn’t know what to do

C.was rich enough to buy one

D.was quite sure of success小题4:The story is mainly about _________________.

A.a useless advertisement

B.how to make an effective advertisement

C.what the merchant did for the umbrella owner

D.how the man lost and found his umbrella