Final answer:
Without additional details about the granite block and the load application area, a specific numerical solution cannot be provided for the magnitude of the load P, the maximum normal stress, or the shear and normal stresses on the critical surface.
Step-by-step explanation:
The student's question relates to shear stress and normal stress in a granite block under a centric load P. To determine the magnitude of P (a), the orientation of the surface where maximum shearing occurs (b), the normal stress on that surface (c), and the maximum normal stress in the block (d), we must apply principles from mechanics of materials.
However, some necessary information is missing from the student's query to provide a complete answer, such as the dimensions of the granite block and the area over which the load P is applied. Normally, the maximum shearing stress occurs at an angle of 45 degrees to the principal stress directions, and the normal stress on that surface would be equal to the principal stress in pure shear. The maximum normal stress in a block is usually the compressive or tensile stress depending on the loading condition.