9. A rectangular rock sample of 6x6x12 cm is loaded by brash platens consisting of many steal wires (see figure below). The total force is 72 kN. Determine, in the simplest possible way, the principal directions and principal stresses. (Neglect the bending resistance of wires.) Determine, in the simplest possible way, principal strains and principal directions of the strain tensor if the rock has Young's modulus of 50*A1 GPa and Poisson's ratio of 0.25. 12 cm 72 kN 6 cm 6 cm