问题 多选题

某人在静止的湖面上某高度处竖直上抛一个铁球,铁球上升到最高点后自由下落,穿过湖水并陷入湖底的淤泥中一段深度(假设泥中阻力大小恒定).不计空气阻力,以v、F、Ek分别表示小球的速度、所受合外力和动能三个物理量的大小.下列图象中能正确反映小球运动过程的是(  )

A.

B.

C.

D.

答案

A、小球在空中先做竖直上抛运动,再做自由落体运动,速度随时间先均匀减小,再反向均匀增加;进入湖水后加速度减小,但仍会做加速运动;进入淤泥后开始减速运动,故速度图象应为A,故A正确,B错误;

C、小球在空中运动过程中只受重力,方向竖直向下;而进入水中后,受力减小,合力方向向下,而进入淤泥后合力向上,故C正确;

D、小球的动能Ek=

1
2
mv2,在空中运动时为匀变速直线运动,v=gt,故动能和时间为二次函数关系,故D错误;

故选AC.

单项选择题
阅读理解

阅读理解。

     A father's job is unique. If parents had job descriptions, mine would read: organize bills, play dates,

laundry, meals, carpool, snacks and outings. The only thing on my husband's description would be the

word "fun" written in big red letters along the top.

    Our parenting styles complement each other. His style is a nonstop adventure where no one has to

worry about washing their hands, or eating vegetables. I'm too busy worrying to be fun. Besides, every

time I try, I am constantly outdone by my husband.

    I bought my children bubble gumflavored toothpaste, and I taught them how to brush their teeth.  

They thought it was neat until my husband taught them how to rinse(濑口)by spitting out water between

their two front teeth like a fountain.

    I tried singing fun songs as I washed behind my children's ears during bath time. They enthusiastically

sang and clapped until their father came in and taught them how to catapult (弹射) the soap into the sink

with the washcloth.

    I took the children for a nature walk to corral (把……赶入……) a slow ladybug(瓢虫)into my son's

insect cage. I was "cool" until their father came home, spent two minutes in the backyard, and captured

a beetle the size of a Chihuahua (吉娃娃,一种产于墨西哥的狗).

     I try to tell myself I am a good parent even if my husband does things I can't do. I can make sure my

children are safe. But I can't wire the VCR so my children can't watch their favourite video.

     I can carry my children in my arms when they are tired and kiss them good night. But I can't flip

them upside down so they can walk on the ceiling or prop them on my shoulders so they can see the

moths flying inside the light fixture.

     I can take them to doctor appointments, but I'll never go into the wilderness to fish. I'll even sit in the

first row of every Little League game, but I'll never teach my children how to hit a home run or slide into

first base.

     I can do a lot of things for my children, but no matter how hard I try, I can never be their father.

1. What's the job of the mother in the passage?

A.  Looking after children,  going shopping and doinghousework.

B. Going shopping and sending her children to school.

C.  Playing with her children and going to school with them.

D. Working in the office and taking care of her children and husband.

2. The father will do the following EXCEPT   ________ according to the passage.

A. going wild to fish with the children

B. making appointments with doctors

C. flipping the children upside down

D. teaching the children how to hit a home run

3. What's the best title for the passage?

A. Mothers Have a Unique Job

B. Children Are Very Important

C. Fathers Have a Unique Job

D. Parents Have Gentle Children