1. A direct shear test was conducted on a cohesion-less soil (C = 0) specimen under a normal stress (σ) of 200 kN/m². The specimen failed at a shear stress (S) of 100 kN/m². Determine the angle of internal friction of the soil (in degrees).

2. A direct shear test was conducted on a cohesion less soil (C = 0) specimen under a normal stress (σ) of 96.6 kN/m². The angle of internal friction (θ) of the soil is 35^o. The specimen fails at a shear stress of ____.