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例1两块质量分别为m_1、m_2的木块,被一根劲度系数为后的轻弹簧连在一起,并在m_1板上加压力F,如图1所示,为了使得撤去F后,m_1跳起时恰好能带起m_2板,则所加压力F的最小值多少?解析:因为撤去F后,m_1跳起时恰好能带起m_2板,故此时弹簧的弹力大小等于m_2g,弹簧处于最长伸长状态,即m_1板此时处于最高点.把m_1、m_2两木块看做一个整体,此整体的重力全部用来产生m_1板的加速度,故有:
Example 1 Two blocks of mass m_1 and m_2, respectively, are connected together by a light spring with a stiffness coefficient and a pressure F is applied to the m_1 plate, as shown in Fig. 1, in order to make F removed. When m_1 jumps, it can just bring up m_2 board, how much is the minimum value of applied pressure F? Analyze: Because after removing F, m_1 jumps to bring up m_2 board, so the elastic force of spring is equal to m_2g, the spring is at The longest stretched state, that is, the m_1 board is at the highest point at this time. Take the m_1 and m_2 blocks as a whole. This overall gravity is used to generate the acceleration of the m_1 board. Therefore: