It was established that the stress state at a point underground was as given below:

_x = 25Mpa, _y = 65Mpa, _z = 75Mpa, _xy = 75MPa, _yz = 50MPa and _xz = 25MPa

(i) Determine analytically, the normal and shear stresses on an oblique plane whose direction cosines are cos = 0.5, cos = 0.5 and cos = 0.5

(ii) Calculate the minimum value of the angle of internal friction required for stability on the plane if cohesion in the rock mass along the plane was given as 1.5MPa