问题 填空题

如图甲所示,物体原来静止在水平面上,用一水平力F拉物体,在F从0开始逐渐增大的过程中,物体先静止后又做变加速运动,其加速度a随外力F变化的图象如图乙所示.根据图乙中所标出的数据可计算出物体的质量为kg,物体与水平面间的动摩擦因数为______.

答案

物体受重力、地面的支持力、向右的拉力和向左的摩擦力,

根据牛顿第二定律得:F-μmg=ma,解得:a=

F
m
-μg,

由a与F图线,得到:0.5=

7
m
-10μ    ①,

4=

14
m
-10μ    ②,

①②联立得,m=2Kg,μ=0.3,

故答案为:0.3.

阅读理解

阅读理解。

                                                                  Rainy Day Fun

     You wake up and the weather is all wet. What are you going to do today? Here are four ideas for you

to try when it's raining cats and dogs.

     Puppet (木偶) show

     You can create your own puppets with things your parents already have around the house. First, you'll

need some old socks or brown paper bags. Then get them decorated. Give your puppets names and funny

voices. You might want to make up a special story for them. Maybe one puppet lost his way home. Maybe

another puppet has superman powers. To make your show even better, use a cardboard box as a stage.

Build a castle Ask your parents for some old sheets, blankets, or comforters. Spread them over chairs or

other furniture to create a top-secret castle. Bring a flashlight, a good book to read, and maybe even a snack.

     Dress-up time

     Both boys and girls can have fun trying on old clothes. Ask your parents to let you try on old hats,

jewelry, shoes, and clothes. Do you want to be a doctor? You can pretend it in a doctor coat. Or maybe you

see yourself as a movie star. Ask your mom for her old dance dresses. Don't forget the earrings and high

heels!

     Say thanks

      Birthdays and holidays are chances for us to thank people who love us. But it can be a special treat to

get a gift or a card on an ordinary day. Think of the people who make you happy and then come up with

a way to show them your care. Use your arts and craft supplies to create a special card. Or ask your

parents to help you make cookies as a gift for that special person. You will be delivering sunshine on a

rainy day!

1. According to the passage, these activities can happen on ______.

A. sunny days

B. rainy days

C. cloudy days

D. windy days

2. When working on the puppet show, children can ______.

A. train their own imagination

B. learn to perform shows on stage

C. know how to deal with others

D. find new ways of creating puppets

3. Which of the following words can be used to describe the kids' castle?

A. Boring

B. Hot

C. Quiet

D. Noisy

4. What can we learn from the passage?

A. You can pretend to be a doctor by trying on your parent's clothes.

B. You can only give a gift or a card to show your care on birthdays or holidays.

C. You can use your own dance dresses to dress up.

D. You can make some gifts to show your care for special persons.

判断题