若是研究力在时间上的积累效果,可用动量定理;若是研究力在空间上的积累效果,可用动能定理.应用它们解决流体问题时,要注意所选的微小变量是Δt(一小段时间)还是Δs(一小段位移)内的变量.1.只能用动量定理例1 太空飞船在宇宙飞行时,它和其它天体的万有引力可以忽略,但是,飞船会定时遇 If the effect of the research force on the accumulation of time, you can use the momentum theorem; if you study the effect of force accumulation in space, the kinetic energy theorem can be used. When applying them to solve the fluid problem, should pay attention to whether the selected tiny variable is Δt (for a short time) or Variables in Δs (a small displacement).1. Only the momentum theorem can be used. Example 1 When a spaceship is flying in the universe, the gravitational pull of it and other celestial bodies can be ignored. However, the spacecraft will meet with