问题 问答题

以20m∕s的初速度竖直向上抛出一物体,质量为0.5kg,空气阻力恒定,小球上升的最大高度为18m.求:

(1)上升过程中克服空气阻力对小球做的功.

(2)小球落回抛出点时的动能.

答案

由题意知,物体最初的机械能E=

1
2
mv2=
1
2
×0.5×202=100J;

上升最大高度处的机械能E′=mgh=0.5×10×18=90J;

空气阻力做负功,所以根据能量守恒W=△E=100-90=10J;

落回抛出点过程中,空气阻力做负功,由能量守恒知:小球落回出发点时的动能E2=90-10=80J.

答:(1)上升过程中克服空气阻力对小球做的功为10J.

(2)小球落回抛出点时的动能80J.

阅读理解

Happiness is for everyone. You don’t need to care about those people who have beautiful houses with large gardens and swimming pools or those who have nice cars and a lot of money and so on. Why? Because those who have big houses may often feel lonely and those who have cars may want to walk on the country roads in their free time.

In fact, happiness is always around you if you put your heart into it. When you are in trouble at school, your friends will help you; when you study hard at your lessons, your parents are always taking good care of your life and your health; when you get a success, your friends will say congratulations to you; when you do something wrong, people around you will help you to correct it. And when you do something good to others, you will feel happy, too. All these are your happiness. If you notice a bit of them, you can see that happiness is always around you.

Happiness doesn’t mean money. It is a feeling of your heart. When you are poor, you can also say you are very happy, because you have something that can’t be bought with money. When you meet with difficulties, you can say loudly you are very happy, because you have more chances to challenge yourself. As the saying goes, life is like a revolving(旋转的)door. When it closes, it also opens. If you take every chance you get, you can be a happy and lucky person.

小题1:When you do something wrong , people around you will    .

A.quarrel with you

B.help you correct it

C.do something wrong like you

D.laugh at you小题2:What will your friends say when you make great progress?

A.Oh, so do I

B.Congratulations!

C.Good luck!

D.Just so-so小题3: Which of the following is NOT true according to the passage?

A.People who have cars would never like to walk in the open air.

B.You can get help from others when you are in trouble.

C.You can still be a happy person even if you have little money.

D.Happiness is always around you though difficulties come towards you.小题4:The passage mainly tells us      .

A.parents always care for our life and health

B.we’re not happy if we meet with difficulties

C.happiness is always around us

D.life is colorful

单项选择题