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有关机械效率的计算在各省市自治区的中考试题中都作为重点内容进行考查。本文结合历年的中考试题就此问题进行归类分析。1 用滑轮组匀速提升物体 例1 如图1所示,用滑轮组匀速起吊800牛的重物G,所用的拉力F=300牛,使物体在1秒钟内上升2米,则拉力做的有用功是__焦,滑轮组的机械效率是__,拉力的功率是__瓦。 (1997,山西省中考题) 分析与解答:用滑轮组提升物
The calculation of mechanical efficiency is examined as the key content in the examination questions in all provinces, municipalities, and autonomous regions. This article combines the examination questions of the past years to classify and analyze this issue. 1 Using pulleys to increase the speed of objects at a uniform speed Example 1 As shown in Fig. 1, use a pulley set to lift the weight of 800 lbs of G at a constant speed. Use a pull force of F = 300 kilos so that the object rises by 2 meters within 1 second. It is __focal, the mechanical efficiency of the pulley is __, and the power of the pull is __W. (1997, Shanxi Provincial Examination Questions) Analysis and Answers: Use pulley block to lift things