Astate of stress that occurs at a point on the free surface of the of a solid body is = 50 mpa σ x , =10 mpa σ y , and = −15 mpa xy τ . a. evaluate the two principal normal stresses and the one principal shear stress that can be found by coordinate system rotations in the x-y plane and give the coordinate system rotations. b. determine the maximum normal stress and the maximum shear stress at this point. c. sketch the rotations and stress magnitudes.