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问题 选择题

如图所示，升降机内的水平地板上，用轻弹簧连接一个的物体，弹簧处于拉伸状态，当升降机以速度v向下做匀速运动时，物体恰好能静止在地板上，若突然发现物体在升降机内向右运动，则升降机的运动情况可能是（　　）

A．保持原来匀速运动

B．向下做加速运动

C．向下做减速运动

D．已停止不动

答案

物体受弹簧的拉力及摩擦力而处于静止状态，弹簧伸长，故拉力向右，摩擦力向左；因物体处于平衡状态故拉力等于摩擦力；

物体向右运动，而在动的瞬间弹力不变，故最大静摩擦力应减小，物体对接触面的压力应减小，即物体应处于失重状态，故升降机加速度应向下，即物体应向下做加速运动，

故选B．

名词解释

Necrotizing external otitis
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单项选择题

Passage One


There are two types of people in the world. Ahhough they have equal degree of health and wealth and other comforts of life, one becomes happy and the other becomes unhappy. This arises from the different ways in which they consider things ,persons, events and the resulting effects upon their minds.
People who are to be happy fix their attention on the convenience of things:the pleasant parts of conversation, the well prepared dishes, the goodness of the wine and the fine weather. They enjoy all the cheerful things. Those who are to be unhappy think and speak only of the opposite things. Therefore, they are continually dissatisfied. By their remarks, they sour the pleasure of society, offend (hurt) many people, and make themselves disagreeable everywhere. If this turn of mind was founded in nature, such unhappy persons would be the more to be pitied. The intention of criticizing and being disliked is perhaps taken up by imitation. It grows into a habit, unknown to its possessors. The habit may be p, but it may be cured when those who have it realize its bad effects on their interests and tastes. I hope this little warning may be of service to them, and help them change this habit.
Although in fact it is chiefly an act of the imagination, it has serious results in life since it brings on deep sorrow and bad luck. Those people offend many others;nobody loves them, and no one treats them with more than the most common politeness and respect. This frequently puts them in bad temper and draws them into arguments. If they aim at getting some advantages in social position or fortune, nobody wishes them success. Nor will anyone start a step or speak a word to favor their hopes. If they bring on themselves public objections, no one will defend or excuse them, and many will join to criticize their wrong doings. These should change this bad habit and be pleased with what is pleasing, without worrying needlessly about themselves and others. If they do not, it will be good for others to avoid any contact with them. Otherwise, it can be disagreeable and sometimes very inconvenient, especially when one becomes mixed up in their quarrels.

We can conclude from the passage that______.

A．we should pity all such unhappy people

B．such unhappy people are dangerous to social life

C．people can get rid of the habit of unhappiness

D．unhappy people can not understand happy persons
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