工程力学习题答案第2章 力系的简化与平衡.docx
第2章力系的简化与平衡2-4 Fr = -1.5i 一 2.0 J (kN) , x = 290mm 2-5 Fa = 54.64kN, Fc = 74.64kN26 Q=173kN, 7 = 95°2-7 P2 = 333.3kN, x = 6.75m2-8 Fa =231N2-9 P = 81kg/2Z?Y32-10 a = arccos I，J2-11 k = 5.61 N/m,、L F 5 . M 厂 F 1 7 M2-12(a) Fa =1qb, FR =qb-a 24 2b R 2 4 2b 3313(b) Fa =-F + -qb, Fb =-F + -qbFAx = l(MkN, FAv = 60kN, MA =220kN.m Fc =120kN(c) FAx = 0, FAv = -2.5kN; Fb = 15kN, FD = 2.5kNFAx = 0, FAy = 2.5kN, MA =10kN.m, Fc =1.5kN(f)，, = 0, FAy = -51.25kN, Fb = 105 kN, FD = 62.5kN2-13(a) FAx = FAv = 0; FBx = -50kN,心v= 100kN *FAx = 20kN, FAy = 70kN; F以=20kN, FBy = 50kN2-14 M = 70.36N m“ Pr A2-15 M =Lr22-16 6底=112.5kN, FAy =112.5kN; FBx = -37.5kN, FBy =-112.5kN;FCx =75 kN, FCy=02-17= 一4.4kN, FAy = 4.0kN;方以=9.34 kN, FBy = 2.67kN;Fc=Fe= 14.9kN, Fd = 4.4kN2.18 FAx = 1.2kN, F/b） =0.15kN; FB =1.05kN, FBC =-1.5kN2-19 F = 1467N2-20 Fac = Fcc = Fgk = Fbd = Fdh = Fhk = -lOkN,其余为零杆。2-21 K = 5.333F （压），& = 2F （拉），F3 =-1.667F （压）2-22 Fcd = 0.866F （压）2-23 %=35.4kN （压），Fef = 30.0kN （拉）2-24 Fdk - IkN （拉）2-25（1） Fr = Fk , Mo = -Fa - Fak（2）左力螺旋，作用于。, 0, 0）点，Fr = Fk, M = -Fak2-26 Fr = 20N ,沿z轴正向，作用线的位置由x。= 60 mm和c = 32.5 mm来确定。2-27 F* = 143.9N, FRy =101 IN, FRz = 516.9NMv =48N.m, Mv =21.07Nm, M_ =19.4N.m xyz2-28M 二=10L4N.m2-29 Fr =-120i-160A;（N）, MA = 7i+ 9j +24 人（N *2-30 M = Fasm/3sm02-31 M x = - F（h - 3r）, M v = F（h + r）, M: 4'2.32 FTl =45.8kN, FT2 = 26.7kN, FNA = 8.901 +16.67 J + 40.0k （kN）2-33 Fa=Fb= -26.39kN（BE）,Fc = 33.46kN（拉）2-34 Fca （压），Fbd = P（cos。sin。）， FBE = P（cos6 + sin9）,Fab = -夜Pcos。2-35 K =5kN（压），F2 二5kN（压）,F. = 7.07kN（压）,F4 =5kN（拉），F5 =5kN（拉），F6 = -lOkN（压）,W2-36厂1 L耳4 二 5己,FT1=（2F1+F2）, /=一（耳+工）一5，/2-37 a 350mm2-38 F = 50 N, 6> = 14308'2-39 （1） M = 22.5Nm； （2） %（=75N,Z74V = 0, %2=50N（3）工=75N,2-40 F = 70.9N ； FAx = -68.4N, FAy = -47.6N; FBx = -207 N , FBy =-19.1N 2-41 /o«=150N, 尸o、,=75N, FOz =500N；Mx =100Nn% Mv =37.5Nm, M_ =24.38Nm2-42 K = lOkN , 与=5kN ,&、. = -5.2kN , FAz = 6kN ； F以=-7.8kN ,FBz =1.5kN2-43 FAx =-2.078kN, FAz = 5.708kN ； FBx =-1.093kN , FBz = 3.（XMkN ；Fcx = -0.378kN , FCz = 12.46kN ；FDx = -6.273kN , FDz = 23.25kN2-44 FCx = -666.7N, FCv = -14.7N, FCz = 12640 N ；FAx = 2667 N, FAy = 325.3N2-45 尸= 200N； FBx = FBz =0； FAx = 86.6N, %, =150N, FAz =100N2-46 F=F5=尸（压），F.=/（拉）,F2=F4=F6=QhrMMM2-47加=二，鼠=；=。，FDy=-一a aaaa2-48七二号；心=。，加=-岁2-49 F=8，Fz=-®Fd，£=-行后，F, = 46Fd , F5 =-F-42FD,Fg=Fd2-50 xc = 10.3 mm, yc = 20.3 mm2-51 xc =90 mm2-522-53 xc = 18.4 mm, yc = 13.2 mm
