Problem 1. The nodal coordinates and the nodal displacements (cm) for some plane-stress elasticity elements are listed below. Calculate the element stiffness matrix and the element stress vector {}. The element thickness is 2cm and the material matrix is 16 4 [D] = 10 4 16 0 0 6. a) X1=2 Y1=0 Ulx = 0.003 Uly =0 X2=1 Y2=1 Uzx = 0.001 Uzy = 0.0015 X3=1 Y3=0 Vix =-0.0003 UsY =0 b) X1=11 Y1=2 Ulx = 0.016 UIY =-0.0008 X2=10 Y2=1.8 Uzx = 0.015 UzY =-0.0006 X3=10 Y3=1.5 Usx =0.014 UBY =-0.0004