问题 选择题

在光滑水平面上有一物块始终受水平恒力F的作用而运动,在其正前方固定一个足够长的轻弹簧,如图,当物块与弹簧接触后向右运动的过程中,下列说法正确的是

A.物块接触弹簧后即做减速运动

B.物块接触弹簧后先加速后减速

C.当弹簧处于压缩量最大时,物块的加速度等于零

D.当物块的速度为零时,它所受的合力为零

答案

答案:B

题目分析:本题属于含有弹簧的问题,要依据胡克定律分析弹簧弹力的变化情况,进而分析合力的变化,根据牛顿第二定律确定物体的运动情况。物块接触弹簧后弹簧的弹力逐渐增大,开始阶段,弹力小于水平恒力F,合力方向向右,与速度方向相同,物体做加速运动,后来弹力大于水平恒力F,合力向左,与速度方向相反,物体开始做减速运动,当弹力与水平恒力F大小相等方向相反时,速度最大,所以物块接触弹簧后先加速后减速,故A错误,B正确;当弹力与恒力F大小相等、方向相反时,加速度为零,此时向右的速度最大,弹簧继续被压缩,加速度反向增大;而当物块的速度为零时,合力向左,加速度向左,不等于零,故C、D错误.所以选B.

阅读理解

阅读理解

     Every girl wants to have a great-looking tattoo (纹身) design that makes them more attractive. Small

and lovely tattoo designs are the path to go for girls planning to get tattooed for the first time.

    Nowadays, more and more females are getting a tattoo inked on their body. In the last fifteen years,

tattoos have grown from being a sign of rebelliousness and trouble to a state of popular acceptance as a

mark of fashion.

    Tattoos are permanent so you need to be sure that you like it before getting one. A great way is to

have small tattoos that look beautiful as well. You can get a cherry blossom tattoo on the foot, perhaps,

a hibiscus flower on the shoulder or a lovely butterfly on the lower stomach; whatever design you choose,

it can definitely add to your attractiveness and charm.

    Deciding to get a tattoo needs careful thought and reflection. Otherwise, you could make some serious

tattoo mistakes. Try to avoid big and obvious designs if possible. Another important part of choosing a

tattoo design is the location. What part of the body do you want it on? Choosing a hidden location can

often make the tattoo the perfect adornment (装饰). As for professional women, tattoos should normally

be where they can be hidden.

    Most importantly, no matter what tattoo design you choose the final goal is that the design should be

something you like. If you are into the tattoo and really feel passionate about it you will carry yourself in

a different manner when you get it inked on your body.

1. A girl wants to have a tattoo in order to ________.

A. show that she is unique              

B. catch up the present fashion

C. become more attractive              

D. have more confidence

2. The underlined word "hallmark" in Paragraph 2 probably means _________

A. feature   

B. exhibition  

C. entertainment   

D. room

3. What did people think of girls who got tattooed in the past?

A. They looked down upon these girls        

B. They thought these girls liked to show off

C. They thought these girls were fashionable  

D. They thought these girls were rebellious

4. What is the author's attitude towards girls' getting a tattoo?

A. He is against girls' doing so    

B. He thinks professional women should not get tattooed

C. He is in favor of it as long as it is done probably

D. He calls on all the girls to do so

5. According to the author, which of the following is the right kind of tattoo that girls should get?

A. Big, beautiful tattoos inked on the back

 B. Small, lovely tattoos inked on the hidden part of the body

 C. Big and fashionable tattoos inked on the foot

 D. Small and beautiful tattoos inked on where it is easy to see

单项选择题