问题 计算题

如下图所示,是2008北京残奥会开幕式最后一棒火炬手侯斌,靠自己双手的力量,攀爬到火炬台底部并最终点燃圣火的照片,该点火仪式充分体现了残疾人自强自立、拼搏向上的勇气和精神。已知他和轮椅总质量为80kg,攀爬高度39m,历时约3min20s。

(1)如果不计机械装置的额外功,求他的平均功率多大?

(2)小明同学看到火炬手攀爬很费劲,想到利用滑轮组可以省力。小明同学如果站在地面上,用如图所示的哪个滑轮组拉起火炬手侯斌最合适,理由是什么?如果该滑轮组机械效率为80%,求小明同学的拉力至少要多大?(g取10N/kg)

(3)求该滑轮组的动滑轮的重力。

(4)若用该滑轮组将质量为100㎏的物体竖直向上匀速吊起,则该情况下滑轮组的机械效率是多少?

答案

(1)P=156W

(2)D滑轮组、拉力方向向下且更省力。 F=250N

(3)G=200N

(4)83.3%

阅读理解

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When it comes to success in business and success in life, there are few qualities as important as confidence. 

People naturally have different levels of confidence. Some have a higher level of confidence than others do, but even those whose confidence is lacking can learn to build their level of confidence and reach their most important goals. Increasing self confidence is one of the most common reasons people give for seeking the help of psychologists and other professionals.

One of the many places where a greater level of confidence is useful is in the workplace. We all know how difficult it can be, for instance, to ask the boss for a raise. This process can be extremely difficult for those who lack confidence in their own abilities. After all, if you are unsure about your own abilities, how will you ever convince your boss that you deserve more money for the work you do?

Even if you are not asking for that big raise, having plenty of confidence in your abilities is important to success. If you are certain of your abilities, chances are that those around you, whether they are your coworkers, your colleagues or your superiors, will see that confidence, and that will help to assure them that you are the best at what you do.

Being thought of as the person to go to, and being seen as an expert in your chosen field, is naturally very important to success on the job. If you can make yourself the person people go to for guidance and advice, you will help to protect yourself from the ever present danger of downsizing. After all, if you are a recognized expert at the office, you will be regarded as an indispensable member of the team.

Having a high level of confidence, after all, does not mean overlooking the places where you could improve. Knowing what you do well and where you need help will help you enjoy increased success and confidence.

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