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在中学物理某参考书中有这样一道题:在互成角度的两个共点力的合成实验中,用A、B两个弹簧秤拉橡皮条的端点,使它伸长到D点,如图1所示.今保持A的示数不变,当角α由图示位置逐渐减小时,欲使D端保持不动,可用的方法是: (A)使B的示数变大,角β变小. (B)使B的示数变小,角β变小. (C)使B的示数变小,角β变大. (D)使B的示数变大,角β变大. 标准答案是C,但有些学生认为应取B,有的书上的答案也取B. 下面用力的三角形法进行作图分析,用F_A、F_B、F分别表示A秤、B秤的示数和合力的数值;用α_0、β_O分别表示F与F_A、F_B的初始夹角. 一、α_0+β_0>90° 1.α_0<β_0时,见图2.
In a reference book of middle school physics, there is such a question: In the synthesis experiments of two common point forces at mutual angles, use the two spring balances of A and B to pull the end of the rubber strip to extend it to point D, as shown in the figure. As shown in Fig.1, the number of A is kept unchanged. When the angle α is gradually decreased from the position of the figure, to keep the D end immobile, the available methods are: (A) Make the number of B large, the angle β Smaller. (B) Decreases the number of B and the angle β becomes smaller. (C) Reduces the number of B, and the angle β increases. (D) Increases the number of B, and the angle β becomes larger. The standard answer is C, but some students think that they should take B, and some of the answers in the book also take B. The following strong triangle method for mapping analysis, use F_A, F_B, F to represent the scale of A scale, B scale, respectively The value of the sum force; α_0, β_O denote the initial angle between F and F_A, F_B, respectively. I. α_0+β_0>90° 1.α_0<β_0, see Figure 2.