Final answer:
Without specific ergonomic guidelines, the recommended weight limit for unloading 30 cm cardboard cubes from a pallet onto a conveyor with twisting involved would err on the side of safety, likely being the lowest weight listed, which is 15 kg.
Step-by-step explanation:
The question presented asks to find the recommended weight limit for the activity of unloading 30 cm cardboard cubes from a pallet onto a conveyor that is 80 cm high. This is a problem that could be related to occupational safety and human ergonomics rather than a straightforward physics calculation. Typically, recommended weight limits for lifting and handling tasks are determined by occupational safety guidelines provided by organizations like OSHA (Occupational Safety and Health Administration) or by using ergonomic assessment tools, like the NIOSH (National Institute for Occupational Safety and Health) lifting equation.
Since the problem doesn't provide specific ergonomic guidelines, and considering that unloading is done with a twisting operation, it is prudent to err on the side of a lighter limit to prevent back injuries or muscle strains. Thus, without further information about the ergonomic standards being applied in the scenario, it is challenging to determine a precise weight limit from the given options (a) 15 kg, (b) 20 kg, (c) 25 kg, (d) 30 kg. However, a common recommendation is to keep the weight lower when a person is twisting during lifting; hence, the safest answer would be the lowest weight possible, which is option (a) 15 kg.