问题 多选题

自行车的大齿轮、小齿轮、后轮三个轮子的半径不一样,它们的边缘上有三个点A、B、C.向心加速度随半径变化图象如图所示,可以知道(  )

A.A、B两点加速度关系满足甲图线

B.A、B两点加速度关系满足乙图线

C.B、C点两点加速度关系满足甲图线

D.B、C点两点加速度关系满足乙图线

答案

A、由于A轮和B轮是皮带传动,皮带传动的特点是两轮与皮带接触点的线速度的大小与皮带的线速度大小相同,

故vA=vB,根据向心加速度的公式a=

v2
r

所以A、B两点加速度关系满足甲图线,故A正确,B错误

C、由于B轮和C轮共轴,故两轮角速度相同,

即ωBC,根据向心加速度的公式a=ω2r

所以B、C点两点加速度关系满足乙图线,故C错误,D正确

故选AD.

阅读理解

阅读理解。

     It's Jim's birthday today.   He is five years old.   He gets many nice birthday presents from his family and one of

them is a big drum (鼓).

     " Who gives him the drum?" his father asks.

     " His grandfather does." answers Jim's mother.

     Jim likes his drum very much.   He makes a noise(噪音) with it,   but his mother doesn't say anything about it. His

father is not at home. He is working in a school. So he doesn't hear(听见) the noise.

     But one of the neighbours doesn't like the noise at all.  So one morning she takes a knife and goes into Jim's room.

Jim is making a noise with the drum. She says to him, "Hello,  Jim, Do you know there is something nice in your drum?

Here is a knife. Open the drum and let's find it."

1. Jim's       gives Jim the drum.       

A. grandfather

B.  father      

C. mother    

D. neighbour

2. Jim's father is         

A. a worker      

B. a  teacher  

C. a cleaner  

D. a shopkeeper

3. The neighbour hates                .   

A. Jim's presents  

B. the drumC. the knife  

D. the noise

4. The neighbour tells Jim                .      

A. to put the drum away (收拾)      

B. to look after the drum 

C. to open the drum with the knife    

D. to make a noise with the drum

5. Which of the following is right?             

A. Jim's grandfather makes the drum.

B. Something is wrong with Jim's father's ears.

C. There is a nice present in the drum.

D. Jim's mother doesn't stop (阻止) the noise.

填空题