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对于一个系统,如果所受外力的合力为零,那么系统所受的冲量合为零,即系统的动量守恒.然而合外力为零,外力对物体系所做的总功却不一定为零.明确这一点,就比较容易判断系统的动量,系统的机械能是否守恒的问题. 例1 如图1,在光滑的水平面上叠放着A、B两物体,B是够长,A、B间有摩擦.现用等大、反向的恒力F1和F2分别拉物体A、B,使得A、B相
For a system, if the resultant force of the external force is zero, then the impulse received by the system is zero, that is, the momentum of the system is conserved. However, when the external force is zero, the total work done by the external force on the object system is not necessarily zero. To clarify this point, it is easier to judge the momentum of the system and whether the system’s mechanical energy is conserved. Example 1 As shown in Figure 1, two objects A and B are stacked on a smooth horizontal surface, B is long enough, and A and B are Friction. Now use equal and opposite constant forces F1 and F2 to pull objects A and B, respectively, so that A and B phases