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本刊1989年第5期刊登的《高中物理综合测试卷》中第六题的答案笔者认为不妥。题目:如图1所示,两平行金属板中间用一长度为d的光滑绝缘杆垂直固定,组成电容器置于水平桌面上,其质量为M。两金属板分别用轻软长导线与电压恒为U的电源两极相连,绝缘杆上套一个质量为m的石墨软环(M(?)m),环与金属板接触后带电量为q。若从环与上金属板接触时的位置静止释放,之后每与金属板相碰的作用时间都为△t。求电容器对桌面的最大压力和最小压
The author of the answer to the sixth question in the “Comprehensive Test Paper for High School Physics” published in the 5th issue of 1989 is not correct. Title: As shown in Figure 1, two parallel metal plates are fixed vertically with a smooth insulating rod of length d, and the capacitors are placed on a horizontal table with a mass of M. The two metal plates are respectively connected to the two poles of the power source with constant voltage U by light soft long wires, and a graphite soft ring (M(?)m) with a mass of m is put on the insulating rod, and the charge quantity is q after the ring contacts the metal plate. If it is released from the position where the ring is in contact with the upper metal plate, then the working time for each collision with the metal plate is Δt. Find the maximum pressure and minimum pressure of the capacitor on the desktop