During an experiment in physics class, a student places a large block on a plank. The student raises one end of the plank to form an incline until just before the block starts to slide down. The block experiences a force of 26 N parallel to the incline and 42 N perpendicular to the incline. What is the coefficient of static friction such that the block stays at rest?

During another experiment, a student places the same large block on a plank. The student raises one end of the plank until the block starts to slide down. Another classmate explains that the block begins to slide because the parallel component of the surface force exerted on the block by the plank increases as the plank is lifted higher. Use mathematical reasoning to explain why the classmate is incorrect.