问题 选择题

如图所示,把一重为G的物体,用一个与时间成正比的水平推力压在足够高而平整的竖直墙壁上,开始时物体的速度为零,从t=0开始,物体所受的摩擦力随时间变化的图象是(  )

答案

答案:D

题目分析:在开始时F较小,所以支持力小,重力大于滑动摩擦力,物体下滑,此时滑动摩擦力为,当滑动摩擦力超过重力物体开始减速,最后静止,所以答案为D

点评:此题考查了牛顿运动定律,判断物体运动情况以及摩擦力的变化。摩擦力分静摩擦力和滑动摩擦力,计算以及分析方法不同

阅读理解

阅读理解

     It may happen sooner or later:when books, toys, songs, snacks, video games, and DVDs have lost

their charm, your child begins to say, "I'm bored!Tell me a story, please."Your mind goes blank and your

child looks at you with great expectation.What should you do?

     You may not realize it, but you have a wealth of stories to share.Personal stories, particularly from your childhood or from books you've read, are good starters.

     Some kids enjoy stories about characters from their favorite books.Whether you take Little Chick on a walk through the barnyard or Firefighter Bob on an exciting drive through the city, don't worry too

much about plot(故事情节). Young kids will enjoy them very much.

     Some kids can appreciate a funny twist, so take a favorite story and turn it upside down by changing

the setting, characters, or plot.Make your child the main character in a funny adventure that fits his

interests.

     When did you lose your first tooth? Who was a favorite teacher of yours? Thinking about Mommy or Daddy as a little kid may excite the imagination.And there's nothing more delightful than a story about the

time a parent did some tricks and their results.Kids delight in these short experiences of a past that are

connected to them.

     When you tell stories, you show how to put words together to make meaning.You share something

new about yourself that your kids may find interesting or exciting and that might be a starting point for

questions and discussions.Above all, you develop a love of words that kids will have for life.

     So take a deep breath and begin:"Once upon a time..."

1. At present most children probably have the least chances to________.

A. watch video games  

B. play with toys

C. have snacks  

D. listen to stories

2. To tell children stories, parents are advised to________.

A. use their imagination to invent some stories

B. learn about their children's interests

C. depend on wide reading

D. choose wellorganized stories in terms of plot

3. From the passage we learn that________.

A. children enjoy hearing stories about their parents

B. children can develop an adventurous spirit by listening to stories

C. children sometimes like to see their parents make mistakes

D. parents can learn to tell lies by telling their children stories

4. What is the biggest benefit that children can get by listening to stories?

A. It shortens the distance between parents and children.

B. It develops the imagination of children.

C. It develops children's love for language.

D. It encourages children to question things.

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