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读了《物理教师》1991年第1期《一道试题的正解》后,颇受启发,该文给出了这道题的一种正确解法,值得借鉴。不过文中有两处明显错误,在此提出商榷。①p.48第5行“A最后的动能增量应为正负功的代数和:fs_1-fs_2=mv~2/2”,A最后的动能增量不仅与摩擦力对A做的正负功有关,还同A与B发生的13次完全弹性碰撞有关,因此,设因与B发生的13次完全弹性碰撞使A获得的动能增加量为ΔE_K,则上式应改为: 这道题确实有一定的难度,我们首先分析一下这道题的物理过程:开始时,车A静止,木块B位于A的正中央以初速v_0=5米/秒向右运动,在第一段时间t_1内,A受到一个水平向右的恒定的摩擦力f作用向右作匀加速直线运动,同时木块B受到一个水平向左的恒定的与f相等的摩擦力作用向右
After reading “Physical Teacher” in the first issue of “A Positive Solution to a Question” in 1991, he was inspired. This article gives a correct solution to this question and is worth learning from. However, there are two obvious mistakes in the text. 1p.48 Line 5 “The last increment of kinetic energy in A should be the algebraic sum of positive and negative work: fs_1-fs_2=mv~2/2”. The last increment of kinetic energy in A is not only the positive and negative work done by friction force A. In addition, it is also related to 13 fully elastic collisions between A and B. Therefore, it is assumed that the total amount of kinetic energy gained by A due to 13 complete elastic collisions with B is ΔE_K. Then the above formula should be changed to: For a certain degree of difficulty, we first analyze the physical process of this problem. At the beginning, the car A is stationary, and the block B is located in the center of A with the initial velocity v_0=5 m/s to the right, during the first time t_1 A is subjected to a constant horizontal friction force F to the right for uniform acceleration and linear motion, while block B is subjected to a constant horizontal and left friction equal to f to the right.