The kinetic energy theorem of mass variable system is derived from the kinetic equation of mass variable body.
从变质量物体的动力学方程出发，推导出变质量系统的动能定理。
2
The kinetic energy theorem of mass variable system is derived from the kinetic equation of mass variable body. The practical value of it is pointed out using an example.
从变质量物体的动力学方程出发，推导出变质量系统的动能定理。指明其实用价值，并举例加以说明。
3
A theorem on kinetic energy for variable mass-point and formula of work of recoil internal forces are given and the reason of soft-rope query is discussed.