问题 多选题
如图所示,一水平传送带以速度v1向右匀速传动,某时刻有一物块以水平速度v2从右端滑上传送带,物块与传送带间的动摩擦因数为μ.则下列说法正确的是(  )

A.如果物块能从左端离开传送带,它在传送带上运动的时间一定比传送带不转动时运动的时间长

B.如果物块还从右端离开传送带,则整个过程中,传送带对物块所做的总功一定不会为正值

C.如果物块还从右端离开传送带,则物块的速度为零时,传送带上产生的滑痕长度达到最长

D.物块在离开传送带之前,可能做匀速直线运动

答案

BD

阅读理解

阅读理解。

     Most dog owners feel that their dogs are their best friends. Almost everyone likes dogs because they try

hard to please their owners. One of my favorite stories is about a dog who wanted his owner to please him.

     One of my friends has a large German shepherd (牧羊狗) named Jack. Every Sunday afternoon, my friend

takes Jack for a walk in the park. Jack likes these long walks very much.

     One Sunday afternoon, a young man came to visit my friend. He stayed a long time, and he talked and

talked. Soon it was time for my friend to take Jack for his walk, but the visitor didn't leave. Jack became very

worried about his walk in the park. He walked around the room several times and then sat down directly in

front of the visitor and looked at him. But the visitor paid no attention. He continued talking. Finally, Jack could

n't stand it any longer. He went out of the room and came back a few minutes later. He sat down again in front

of the visitor, but this time he held the man's hat in his mouth.

     German shepherds aren't the only intelligent dogs. Another intelligent dog is a Seeing Eye dog. This is a

special dog which helps blind people walk along the streets and do many other things. We call these dogs

Seeing Eye dogs because they are the "eye" of the blind people and they help them to "see". Seeing Eye dogs

generally go to special schools for several years to learn to help blind people.

1. The writer tells the story about the dog Jack to show that _____.

A. it, like many other dogs, always tried to please its master

B. it, unlike many other dogs, always wanted its master to please it

C. it was more intelligent than many other dogs

D. it was the most faithful dog of his friend's

2. Jack came to sit in front of the visitor in order to _____.

A. please him

B. be pleased

C. ask him to leave immediately

D. invite him for a walk

3. The sentence "Finally, Jack couldn't stand it any longer." means _____.

A. Jack could no longer put up with the visitor

B. Jack could no longer stand but he might sit down

C. Jack was very tired and wanted a rest

D. Jack was very angry with the visitor

4. Which of the following titles would be the best for the passage?

A. Dogs-A Great Help to People

B. Dogs-Our Faithful Companions

C. An Introduction to Dogs

D. Famous Dogs in Germany

单项选择题 A1型题