Final answer:
The capacity of stair treads to sustain a specific load is determined by engineering and construction standards. If a 120-pound figure skater is supported by a blade area of 2 square inches, exerting 30 lb/in², 4 square inches should support 120 pounds. However, the actual required load capacity will be based on specific building codes.
Step-by-step explanation:
The question refers to the capacity of stair treads to support a certain amount of concentrated load. This is relevant to fields of engineering and architecture, particularly when considering building codes and safety standards for construction. The exact load that 4 square inches of stair tread should support can depend on these standards, which can differ by jurisdiction. The example provided about the weight distribution of an elephant and a figure skater illustrates how pressure is calculated. Using the elephant example, if an elephant's foot has a footprint area of 250 in² and exerts about 14 lb/in², we know that the load supported by one foot is 14 lb/in² × 250 in² = 3,500 pounds.
In a similar way, we can analyze how much load 4 square inches should support. If a skater weighing 120 lbs has skate blades with an area of 2 in² each (supporting half the body weight), then each blade supports 60 pounds, resulting in a pressure of about 30 lb/in². If stair treads are expected to support pressures similar to the skater's blades, then the load for 4 square inches would be 4 in² × 30 lb/in² = 120 pounds. However, engineering standards for construction will dictate the specific load capacity required, and it is typically much higher to ensure safety and account for variations in use and weight distribution.