题干

如图斜面ABC,AB段是光滑的,BC段是有摩擦。某物体从A点由静止开始下滑,当滑至C点时恰好停止,则下列说法正确的是                         (   )

A:BC段的长度总大于AB段,但BC段的动摩擦因数越大时,BC段的长度越接近AB段的长度

B:BC段的长度总大于AB段,但BC段的动摩擦因数越小时,BC段的长度越接近AB段的长度

C:在θ角小到一定值时,只要BC段的动摩擦因数适当,AB段的长度可以大于BC段的长度

D:θ=300时,选择适当的动摩擦因数,可使得AB的长度大于BC段的长度

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答案(点此获取答案解析)

C

同类题3

阅读下面短文,从短文后各题所给四个选项(A、B、C和D)中,选出可以填入空白处的最佳选项,并在答题卡上将该项涂黑。

    A group of frogs were traveling through the woods, and two of them fell into a pit(深坑).When the other frogs saw how 1 the pit was, they told the two frogs that they2as well wait to die. The two frogs ignored the comments and tried to jump3 the pit with all their4 The other frogs kept telling them to5,and that they were as good as dead. Finally, one of the two frogs listened to what the other frogs said and6.He fell down and died.

    The other frog continued to jump 7 and try his best. Once again, the crowd of frogs shouted at him to stop the8and just die. He jumped even harder and finally9 it. When he got out, the other frog said," Didn't you 10us?" The frog explained to them that he was a little 11.He thought they were 12 him the entire time rather than advising him to stop the pain of struggle.

    This story teaches us two13: First, there is the power of life and14 in words. An encouraging word to someone who is15 can lift him up and help him make it through. Second, a(n) 16 word to someone who is down can be what it takes to kill him.

Be careful of 17 you say. Speak positively to those who cross your path.The power of words is so great; it is18 hard to understand that an encouraging word can go such a(n) 19 way. Anyone can speak words that tend to rob(掠夺)another of the20 to continue in difficult times.The individual who will take the time to encourage another is special.

同类题5

阅读短文,回答问题

相信你,能行!

    “气死我了,成绩差还要偷看,作弊!”数学老师边嚷边推着两名学生走进了办公室。班主任一看,是一班两名“双差生”,他们垂着头。涨红着脸,胆颤心惊地等着训斥。看到他们的样子,班主任克制住火气,把他俩拉到身边,亲切地说:“是不是考试时作弊呀?那好,老师就给你俩讲一个‘作弊’的故事”。

    “十几年前,有一个孩子成绩比你俩还差,又调皮捣蛋,是个十人看见九摇头,阎王看见伸舌头的讨厌鬼。作业、考试不是抄袭就偷看作弊,老师们对他也没办法。五年级时,新来了一名语文老师,这个老师给他们上的第一堂课就是进行一次摸底测验。”

    “那他又偷看了?”李峰已没有了先前恐惧,插话道。

    “是啊,他还作弊。可正当他拿出一本作文选准备抄作文时,却发现新的语文老师竟然站在他的身后,而且用一双威严的眼睛盯着他!”

    “惨了,惨了,这下是吃不了兜着走,他有苦受了。”须军也被故事吸引,竟为故事中的主人公担忧起来。

    “是啊,当时他心里也这么想。可是新的语文老师却没有发火,而是用一种亲切的、充满信任的眼光看着他,一只手轻轻地把作文选合上,尔后在他的肩头轻轻一拍,一字一顿地说:“好好写,自己写,相信你,能行!”

    “这老师多好啊!”两孩子轻声感叹着。

    “是啊,那孩子心里激动极了,鼻子酸酸的,直想哭。因为读书至今,他从没有被一位老师这样真诚地信任过!他得一下子有无尽的自信和动力在他身上聚集:老师相信我能,我一定能行!”

    “后来,他把老师的那句‘相信你,能行!’的话作为自己的座右铭,痛改前非,成绩一点点赶了上来。几年过后,在他的努力下,他终于从一名差生成长为一名光荣的人民老师。老师的故事讲完了,我觉得你俩一点儿也不比故事的‘他’笨,只要他们能相信自己的能力,努力学习,克服缺点,老师坚信,你们一定不会比‘他’差!你们说行不行?”

    “行!”两人异口同声地高声回答,走出办公室,去向数学老师认错了。几天后,他们的课桌上写着五个字:“相信你,能行!”