解小车受力如图,由 ΣX=0,Fr- P sina=0 ΣY=0,FMA+FN- P cosa=0 MA(F)=0, FNB(a +b) Fnd ep sina -al 解得 =196.6kN,FB=90.12kN,FA=47.54kN 3.9已知P=30kN,F 4kN,a=0.2m,b=0.1m,c 0.05m,l=5m; 求飞机匀速航行时,阻力Fx, 机翼升力F1y尾部升力F2ye 解飞机受力如图所示,由 题3.9图 ∑X=0,Fx-F=0 ΣY=0,F1y+F2y-P=0 EMA(F)=0, (a+LF2y-Pa- Fb-FIc =0 F2=4kN,F12=28.731 3.10已知P1,P2,a,b,c; 求轴承A、B处的支座反力。 解起重机受力如图,由 EMB(F)=0, FNAc-Pla-P26=0 ΣX=0,-FMA+FBx=0 ΣY=0,FB-P1-P2=0 解得FNA=FBx= Pla+ p2b =P1+P2 题3.10图 35