40cm=0.4m80cm=0.8m300cm=3mr内=0.2mr外=0.4mV外=0.2*0.2*3.14*3=0.3768V内=0.4*0.4*3.14*3=1.5072V混=1.5072-0.3768=1.13041.1304*100=113.04M^3
