2-3 FM=-20kN. FM =-10kN Fm=10kN 10KN F 20×10°N 100MPa , 200mm 10KN 10×103N 20KN N2 33.3MPa 300mm F310×103N n3 = 25MPa A3 400mm2-3 FN1 = −20k N, FN 2 = −10k N, FN3 = 10k N MPa m m N A FN 100 200 20 10 2 3 1 1 1 = − −   = = MPa m m N A FN 33.3 300 10 10 2 3 2 2 2 = − −   = = MPa m m N A FN 25 400 10 10 2 3 3 3 3 =   = = 10kN (+) (-) 10kN 20kN