题干

如图所示,一根不可伸长的轻绳两端分别系着小球A和物块B,跨过固定于斜面体顶端的小滑轮O,倾角为30°的斜面体置于水平地面上.A的质量为m,B的质量为3m.开始时,用手托住A,使OA段绳恰处于水平伸直状态(绳中无拉力),OB绳平行于斜面,此时B静止不动.将A由静止释放,在其下摆过程中,斜面体始终保持静止,下列判断中错误的是(   )

A:物块B受到的摩擦力先减小后增大

B:地面对斜面体的摩擦力方向一直向右

C:小球A所受重力的功率先增大后减小

D:小球A的机械能先增大后减小

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D

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Finding the Real You

    Psychometric testing—personality testing—has been very popular nowadays as studies show their results to be three times more accurate in predicting your job performance. These tests are now included in almost all graduate recruitment (招聘) and are widely used in the selection of managers.

    The most popular of these personality tests is the Myers-Briggs Type Indicator (MBTI). It is based on the theory that we are born with a tendency to one personality type which stays more or less fixed throughout life. You answer 88 questions and are then given your “type”, such as Outgoing or Quiet, Feeling or Thinking.

    Critics of personality testing raise doubts about “social engineering”. Psychologist Dr. Colin Gill warns that the “popular” personality traits (特性) have their disadvantages. “People who are extremely open to new experiences can be butterflies, going from one idea to the next without mastering any of them.” However, the psychometric test is here to stay, which may be why a whole sub-industry on cheating personality tests has sprung up. “It's possible to cheat,” admits Gill, “but having to pretend to be the person you are at work will be tiring and unhappy and probably short-lived.”

    So can we change our personality? “Your basic personalities fixed by the time you're 21,”says Gill, “but it can be affected by motivation and intelligence. If you didn't have the personality type to be a doctor but desperately wanted to be one and were intelligent enough to master the skills, you could still go ahead. But trying to go too much against type for too long requires much energy and is actually to be suffered for long. I think it's why we're seeing this trend for downshifting—too many people trying to fit into a type that they aren't really suited for.”

    Our interest in personality now exists in every part of our lives. If you ask an expert for advice on anything, you'll probably be quizzed about your personality. But if personality tests have any value to us, perhaps it is to free us from the idea that all of us are full of potential, and remind us of what we are. As they say in one test when they ask for your age: pick the one you are, not the one you wish you were.