问题 多选题

如图,在一个粗糙水平面上,彼此靠近地放置两个带正电荷的小物块.由静止释放后,两个物块向相反方向运动.在物块的运动过程中,下列表述正确的是(  )

A.两个物块的库仑力为斥力,且大小相等

B.物块受到的库仑力逐渐减少

C.库仑力对物块不做功

D.两个物块的电势能逐渐增大

答案

A、同种电荷相互排斥,故两个物块的库仑力为斥力,根据牛顿第三定律,大小相等,故A正确;

B、由于间距逐渐增加,故库仑力逐渐减小,故B正确;

C、两物块之间存在库仑斥力,与位移同方向,故对物块做正功,故C错误;

D、电场力做功等于电势能的减小量,库仑力对物块做正功,故两个物块的电势能逐渐减小,故D错误;

故选:AB.

阅读理解

阅读理解。

     "There are 365 days in a year. We sleep 8 hours a day,so we have 122 days for sleeping. Then our

work time has 243 days left. But there are 52 weekends in a year. Each weekend is two days. We lose

another 104 days a year for work. It takes us about one hour to have breakfast and supper. This comes

to 15 days over a year. But we can' t work all that time--we need a holiday. Let' s say we have three

weeks' holiday. We don't work all day. Four free hours each evening takes up 61 days. We have to

remember that we get 2 days' holiday at Easter, 3 at Christmas and 1 at the New Year.

     There are also 4 Bank holidays. Take those 10 days away and we have 32 days for work. But then

we have one and a half hours' lunch every day, and half an hour' s coffee break. That comes to 30 days

a year. This means that we have only a few days left for work every year!

1. —How many days do we sleep in a year?—There are_____days. 

A. 365            

B. 122            

C. 8            

D. 52   

2. We spend 15 days on_____.     

A. rest          

B. coffee break  

C. lunch        

D. breakfast and supper  

3. Which of the following is true?                      

A. Each weekend is one day.      

B. We have 61 days for .free time.

C. We get 3 days' holiday at Easter.

D. Coffee break takes us one hour.  

4. According to the passage, we know that we don' t have _____ time to work every year.     

A. much too    

B. so many      

C. too much      

D. too many

5. The writer means_____.

A. we should know the numbers  

B. time is important and we'd better not-waste it.

C. we need more holidays      

D. a few days for work is enough

选择题