Final answer:
A Personal Fall Arrest System (PFAS) must be strong enough to withstand the impact energy of an employee falling six feet, which is determined by the change in kinetic energy as the person falls.
Step-by-step explanation:
When stopping a fall, a Personal Fall Arrest System (PFAS) must withstand the potential impact energy resulting from an employee free falling a distance of six feet. This potential impact energy is derived from the work-energy principle, stating that the work done, in this case by the PFAS when stopping a fall, is equal to the change in kinetic energy. Since the kinetic energy of a falling body increases with the square of its velocity, which in turn depends on the falling height and acceleration due to gravity, a PFAS must be able to convert the energy of a falling employee from kinetic energy to another form, such as elastic potential energy in the system's webbing or shock absorbers, to gently halt the fall.
For example, if a 60.0-kg person falls from a height of 3.00 m and stops abruptly, the force exerted on their knees or the absorbing system can be quite substantial. The PFAS, in reality, is designed to slow the fall over a certain distance, dissipating the energy more safely. The actual force needed to stop a fall also depends on the stopping distance of the system, which is a crucial factor in reducing the force exerted on the employee's body.