Final answer:
The normal and shear stresses at point A in a wood beam can be calculated using transformation equations for stresses, which take into account the load applied to the beam and the angle of the wood grains to the horizontal.
Step-by-step explanation:
To determine the normal and shear stress at point A in a wood beam subjected to a load of 12kN with the wood grains at an angle of 25 degrees to the horizontal, we should apply concepts from mechanics of materials. The stresses on an inclined section of the beam due to an axial load can be found by considering equilibrium and compatibility conditions and by using the transformation equations for stresses.
The normal stress (sigma) on a plane can be found using the formula sigma = P / A, where P is the load on the beam and A is the cross-sectional area perpendicular to the load. The shear stress (tau) on a plane can be calculated by the formula tau = V / A, where V is the shear force and again A is the relevant cross-sectional area.
To find the normal and shear stress specifically at the angle given, one needs to use the transformation equations for normal and shear stress which take into account the angle of the grains to the horizontal direction. However, without the exact cross-sectional dimensions of the beam or details on how the load is applied (uniformly distributed, concentrated at a point, etc.), we cannot provide numerical values for these stresses.