Final answer:
The resultant pressure force on a submerged body in a fluid with no shear forces acts perpendicular to the surface of the body, due to the nature of fluids at rest exerting pressure equally in all directions.
Step-by-step explanation:
When a body is submerged in a fluid with no shear forces present, the resultant pressure force on the body acts perpendicular to the surface of the body. This perpendicular direction is due to the fact that fluids at rest can only exert normal forces; they cannot exert shear forces. The fluid pressure, being a scalar quantity, is exerted equally in all directions and is always directed normally to surfaces in contact with the fluid. Therefore, the correct answer to the student's question is (c) Perpendicular to the surface of the body.
In addition, when considering the effects of pressure in fluids, it is crucial to remember that pressure increases with depth, leading to a net upward, or buoyant force, due to the higher pressure exerted on the bottom surface of the submerged body compared to the top surface.