问题 问答题

如图所示,质量为m1=0.4Kg的物体甲通过二段轻绳和一个轻质细弹簧悬挂在结点O.轻绳OB水平且B端与放置在水平面上质量为m2=0.5Kg的物体乙相连,轻弹簧OA与竖直方向的夹角θ=370,物体甲、乙均处于静止状态.(已知:sin37°=0.6,cos37°=0.8,tan37°=0.75;g取10m/s2.)求:

(1)若轻弹簧的劲度系数为K=500N/m,则轻弹簧的伸长长度是多大?

(2)物体乙受到的摩擦力是多大?方向如何?

(3)若物体乙的最大静摩擦力等于12N,则欲使物体乙在水平面上不滑动,物体甲的质量m1最大不能超过多少?(将AO替换为细绳,保持O点位置不变)

答案

(1)对物体受力分析,如图所示:

由几何关系可知:弹簧的拉力T0A=

m1g
cosθ
=
5
4
m1g=5N  

由胡克定律可知:X=

TOA
K
=0.01m

(2)由图可知:OB的拉力TOB=m1gtanθ=

3
4
m1g=3N,而乙在水平方向受力平衡

所以乙受到的摩擦力f=TOB=3N 

 方向水平向左

(3)由题意及(2)的解答可知:

TOB=

3
4
m1g=fm=12N

解得甲的质量:

m1=1.6kgN,即物体甲的质量m1最大不能超过1.6kg  

答:(1)轻弹簧的伸长长度是0.01m;

(2)摩擦力为3N,方向水平向左;

(3)甲的质量不能超过1.6kg.

阅读理解

Charles Chaplin was born in London on April 16, 1889. His parents were music hall actors. The Chaplin family were very poor, and life was difficult in London. Charlie, as he was called, used to do his mother’s job in the theatre when she was ill.

When he was only 17 years old, Chaplin got his first real job as an actor. What he did was to do silly things to make people laugh in the theatre. Seven years later he went to the USA. And over the next four years, he formed his own way of art. He developed the character (~J ~, )of a homeless gentleman which became very popular.

From the 1920s to the 1950s, Chaplin made his most famous films. The film Modern Times (1936) shows his care about the modern industry workers. Many of his films describe the poor life and hard time of the working people during that period.

Although Charlie Chaplin was British, he lived in the USA until 1953. But he never got US nationality. Then Chaplin, his wife’ and his five children had to move to Switzerland where he lived until he died. When he was 83 years old, he won his only Oscar for the music he wrote for the film Limelight. He was named Sir Charles Chaplin at the age of 85. Charlie Chaplin died in Switzerland on December 25th, 1975.

小题1: Chaplin used to __ when his mother was ill.

A.look after her

B.do the housework

C.do his mother’s job

D.do his father’s job小题2:From Paragraph 2, we can know that __

A.Chaplin went to the USA when he was 24 years old ~

B.Chaplin became famous when he was 17 years old

C.people liked Chaplin because he was a homeless gentleman

D.Chaplin did many silly things to make people laugh in the street小题3:  __ Chaplin made his most famous films.

A.From 1889 to 1936

B.From the 1920s to th~ 1950s

C.From 1953 to 1975

D.From the 1950s to the 1980s小题4: We can infer.from the passage that Chaplin left the USA because of __

A.his family

B.his work

C.the US government

D.the Swiss government小题5: Chaplin won the Oscar for __ when he was 83 years old.

A.the acting

B.the art

C.the film

D.the music

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