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在初中物理“机械效率”的教学过程中,许多学生不能正确理解“总功”的概念,从而不能正确地计算出机械效率。在学过有关内容以后,我们对学生作了一次测试,其中有这样一道题目: 如图,一重量为G的物体在沿斜面向上的拉力作用下,从斜面底部运动到顶端,设斜面长为L,高为h,拉力为F,物体受到的摩擦力为f,则斜面的机械效率为① Gh/FL.②Gh/(F-f)L.③Gh/(F+f)L.④Gh/fL. 学生选答案①的不足30％,选②或③的占70％以
In the teaching process of junior high school physics “mechanical efficiency”, many students cannot correctly understand the concept of “total work” and thus cannot correctly calculate the mechanical efficiency. After studying the relevant content, we conducted a test on the students, among which there is such a problem: As shown in the figure, an object with a weight of G moves from the bottom of the inclined surface to the top under the pulling force along the oblique surface, and the length of the inclined surface is L. The height is h, the tension is F, the friction force of the object is f, then the mechanical efficiency of the slope is 1 Gh/FL.2Gh/(Ff)L.3Gh/(F+f)L.4Gh/fL. Less than 30% of answer 1 and 70% of choice 2 or 3