1 计算斜面：η =W有用/W总=Gh/FL×100%2 定滑轮：η =W有用/W总=Gh/Fs=Gh/Fh=G/F×100%3 动滑轮：η =W有用/W总=Gh/Fs=Gh/F2h=G/2F×100%4 滑轮组；η =W有用/W总=Gh/Fs=Gh/Fnh=G/nF×100%
有用功/总功
