题干

如图所示,一轻质细绳的下端系一质量为m的小球,绳的上端固定于O点。现用手将小球拉至水平位置(绳处于水平拉直状态),松手后小球由静止开始运动。在小球摆动过程中绳突然被拉断,绳断时与竖直方向的夹角为α。已知绳能承受的最大拉力为F,若想求出cosα值,你有可能不会求解,但是你可以通过一定的物理分析,对下列结果自的合理性做出判断。根据你的判断cosα值应为(   )

A:

B:

C:

D:

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D

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阅读理解

    The world seems gloomy(阴沉的)and gray when you're feeling blue. In fact, being down might even affect how you perceive(感知)the color blue. A recent study about color was published in the journal Psychological Science. It shows a direct connection between a person's ability to perceive color and their emotions.

    Psychologists have long known that emotions can affect the way people perceive things. That's in part because chemicals from your brain might affect how you process what you see. “Color is such an important part of our experience,” says lead author Christopher Thorstenson, a psychologist at the university of Rochester, in New York. There's reason, he says, that sad people commonly describe the world as “colorless” and “gray”, and happy people use words like “bright” and “colorful”.

    In the experiment, the researchers randomly assigned people to one of two groups. People in the “sadness” group watched a sad scene from The Lion King. Those in the “amusement' group watched a comedy.

    Everyone was then asked to look at red, yellow, green, and blue patches(斑点)that had been changed to a grayish color. “Some of the patches are pretty difficulty to make out,” Thorstenson admits he says it takes some time to figure out their shade. People were scored on how accurate their color perception was. Then they completed an emotional evaluation.

    The result? Sad people had a hard time seeing the difference between shades along the blue-yellow color axis(色轴). But they did no have problems seeing colors in the red-green spectrum(光谱). Thorstenson says this could be the result of an evolutionary need to see red as a response to anger.

    Thorstenson says these results highlight the possible important of dopamine in sight. Dopamine is a chemical that sends signals to the brain. Researchers are hoping to focus more on dopamine in the future. “We know dopamine affects how we see colors, too,” Thorstenson says “How we feel can really influence how we see the world around us” he says.