Final answer:
The safety guideline for ladder usage is that it should extend at least 3 feet above the elevated platform. The physics problem described involves calculating forces at the base of a ladder in static equilibrium, which is unrelated to the safety guideline.
Step-by-step explanation:
The question presented seems to be mixing two unrelated topics: ladder safety and physics problem involving forces. Regarding ladder safety, the general guideline is that a ladder should extend at least 3 feet above a roof or other elevated platform to ensure stability and safe mounting and dismounting. This information pertains more to health and safety regulations than to high school physics.
In a physics context, the question provided is about calculating the normal reaction and friction forces at the base of a ladder. This involves understanding the principles of static equilibrium and applying Newton's laws of motion. The student is typically required to represent the forces mathematically and solve for the unknowns using moments and force balance equations.
The specific physics problem mentioned involves a 70.0 kg person placing a 6.00 m aluminum ladder against a house, with considerations for the position of the ladder, the center of mass, and the frictionless contact at the top. To solve this, the forces at the top and bottom of the ladder must be calculated, which is not directly related to the initial question about ladder extension above a roof.