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质点组动量定理,即质点组所受外力的冲量等于质点组动量的增量。应用这个定理能使高中不少繁杂物理题的运算简化到令人叫绝的地步。笔者认为,对于仅有两个“质点”组成的系统,所受外力又在一条直线上的“系统动量定理”,可以作为一种解题方法介绍给有兴趣的学生,启发他们的智慧,提高解题能力,以下列举两例供参考。例1.质量为m的金属球和质量为M的木块用轻绳连接,从静止开始它们以加速度a在水中下沉,经时间t_1细绳断了,金属球和木块分开,再经t_2木块停止下沉并开始上浮,则此时刻金属球速度是多少? 这道题若用通常的解法,其运算十分复杂。 [巧解] 把金属球和木块作为一个系统,若绳不
Particle group momentum theorem, that is, the impulse of the external force of the particle group is equal to the increment of the momentum of the particle group. Applying this theorem can make the calculation of a lot of complicated physics problems in senior high school simplified to the point where it is absolutely amazing. The author believes that for a system consisting of only two “mass points”, the “system momentum theorem” subjected to external forces in a straight line can be used as a problem-solving method to introduce to interested students, inspiring their wisdom and improving Problem solving ability, the following enumerated two cases for reference. Example 1. Metal balls of mass m and blocks of mass M are connected by light ropes. From a standstill they sink in water with acceleration a, and after time t_1 the string breaks, the metal ball separates from the wood block, and then The t_2 block stops sinking and starts to float. What is the speed of the metal ball at this moment? If this problem is solved by ordinary methods, its operation is very complicated. [Qiao Qiao] Use metal balls and wooden blocks as a system, if the rope is not