问题 选择题

在第16届广州亚运会上,中国跳水队包揽全部10枚金牌。如图是某跳水运动员最后踏板的过程:设运动员从高处落到处于自然状态的跳板(A位置)上,随跳板一同向下运动到最低点(B位置)。对于运动员从A位置运动到B位置的过程中,下列说法正确的是

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A.运动员到达最低点时处于超重状态

B.在这个过程中,运动员的加速度一直在增大

C.在这个过程中,运动员的动能一直在减小

D.在这个过程中,跳板对运动员的支持力一直做负功

答案

AD

分析:根据运动员的受力变化,可知运动员加速度的变化;根据加速度可知物体速度的变化,即可得出动能的变化;

当物体加速度向上时,物体即处于超重状态,而加速度向下时,物体处于失重状态;

当力与运动方向相反时,力即做负功;当力与运动方向相同时,力即做正功.

解答:解:人在A点时,弹力为零,当人从A到B的过程中,跳板的形变增大,则弹力增大;因弹力开始时小于重力,故在运动过程中合力减小,加速度减小;

而当弹力等于重力时,人仍有速度,跳板继续下降,弹力增大,弹力大于重力,合力增大,加速度增大,故在整个过程中加速度是先减小后增大;最低点时合力向上,故人处于超重状态;因加速度开始时向下,与运动方向相同,故物体的速度增大,然后再减小,故动能也是先增大后减小;

故A正确,BC错误;

在整个过程中,支持力向上,而物体一直向下运动,故支持力做功为负,故D正确;

故选AD.

点评:本题很多同学极易忽视运动过程,解题时一定要结合受力分析,确定力和运动的关系,从而明确物体的运动过程.

阅读理解

In my experience, one of the greatest reasons of unhappiness is the difficulty we have in accepting things as they are.When we see something we don’t like, we wish it could be different–we cry out for something better.That may be human nature, or perhaps it’s something that has been grown in our culture.

The root of the unhappiness isn’t that we want things to be different, however, it’s that we decided we didn’t like it in the first place.We’ve judged it as bad, rather than saying, “It’s not bad or good, but it just is.”

Here is an example.I have written a paper, A Beautiful Method to Find Peace of Mind.Quite a few people think it bad after reading it because I think people should expect things to go differently than you planned, and that you should accept that, instead of encouraging people to change themselves or the environment as much as possible.You could accept it as the way the world works–as the way things actually are.And try to understand why that is, and follow it, as it is.

This can be useful to whatever you do: whether it be how other people act at work, how politics works and how depressing the news media can be.Accept these things as they are, and try to understand why they’re that way.

It’ll save you a lot of sadness because you’ll no longer say, “Oh, I wish things didn’t go bad!”

If you really understand what I mean, you can try a different way to live in this world:accept, and understand.It might lead to some interesting results.

1.What is the major reason why we feel unhappy in the writer’s opinion?

A.We are never satisfied with ourselves and the environment around us.

B.When we see something that makes us unhappy, we don’t know what to do.

C.We feel hard to accept the way things happen themselves.

D.No matter how happy we are, we never want to be happy.

2.What do you think the writer may say to himself when he meets something unhappy?

A.How could I have made such a stupid mistake?

B.I should have done better.It’s all my fault.

C.Why is it all against my plan? It can’t be so bad.

D.Well, I know all is what it is meant to be.Take it easy.

3.Why do some people think badly of the writer’s new paper after reading it?

A.The writer hasn’t shown an encouraging attitude in his paper.

B.The writer asks people to try to make things better.

C.The writer reminds the people that things will go exactly as you’ve planned.

D.The writer doesn’t think it a good idea to accept the things go naturally.

4.The statements below are based on the writer’s points of view, EXCEPT_______

A.Unhappiness may be caused by human nature that we always want things to be better.

B.Why we don’t like the thing is that we have regard it as bad in the beginning.

C.The news media shouldn’t be so depressing if the reporters worked harder.

D.The best way to avoid feeling unhappy is to accept the things as they are.

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