五幅图中,图3、图5比较少见,其他三幅在各种物理课本中都常可看到。因此,对第1题,很多人可能以为答案是D,即3、5两幅图错了。其实,错误的是图2和图3,正确的答案应该是B。大家知道,在题目所说的理想条件下(即不计滑轮质量,没有摩擦),跨过滑轮的绳子上两边的张力是相等的。而且,动滑轮上绳子与竖直线所成的角度两边也应该是相等的,不然的话,水平方向上的力就不平衡,动滑轮会向某一侧移动。因此,图2是错误的,这里两边角度画成不相等了。图1中两边角度虽不相等,但这是一个定滑轮,如果滑轮与横梁的固定联结足够结实的话, Of the five maps, figures 3 and 5 are relatively rare, and the other three are often seen in various physics textbooks. Therefore, for the first question, many people may think that the answer is D, that is, 3 and 5 are wrong. Actually, the mistakes are figures 2 and 3, and the correct answer should be B. As we all know, under the ideal conditions stated in the title (ie, regardless of the quality of the pulley, there is no friction), the tension on both sides of the rope across the pulley is equal. In addition, the angle between the rope and the vertical line on the moving pulley should also be equal. Otherwise, the force in the horizontal direction will be unbalanced, and the moving pulley will move to one side. Therefore, Figure 2 is wrong, where the two sides are not drawn equal. Although the angles on both sides are not equal in Figure 1, this is a fixed pulley if the fixed connection between the pulley and the beam is strong enough.