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对本刊1987年第10期所发表的《是(v-v_0)还是(v+v_0)——关于动量守恒定律公式中符号的选取》一文,先后收到江西万载双桥中学丁剑锋,黑龙江密山县兴凯湖农场一中韩济湘等提出有误,现将来稿摘登如下: 我认为文中的“解法2”是错误的。单从答案“v=mv_0/M”来看,如果字母带正负号,则v与v_0同号即方向相同,而这显然就是错误的。造成这个错误的原因是认为粒子相对地面来讲速度为(v-v_0)。而实际上,对于相对速度,存在以下的关系: 甲对乙的速度+乙对丙的速度=甲对丙的速度 (在上式中的速度都为矢量) 根据以上的这个关系,则可得:
For the article “Yes (v-v — 0) or (v + v — 0) — Selection of Symbols in the Formula of the Law of Conservation of Momentum” published in the 10th issue of this magazine in 1987, we received Ding Jianfeng, Heilongjiang, Shuangqiao Middle School in Jiangxi Province. There are some mistakes in the proposed Xingkaihu Farm No. 1 China and South Korea and Hunan Jixiang, etc. The future drafts are excerpted as follows: I think the “solution 2” in the text is wrong. From the perspective of the answer “v=mv_0/M”, if the letters are signed, then v and v_0 have the same direction, which is obviously wrong. The reason for this error is that the particle is considered to have a velocity (v-v_0) relative to the ground. In fact, for relative speed, there are the following relations: The speed of A to B + the speed of B to C = The speed of A to C (the speeds in the above equation are all vectors) According to the above relationship, you can get :