Final answer:
Gas turbines have low mechanical efficiency because roughly two-thirds of the power output is used to operate the air compressor, highlighting the energy losses in thermal processes compared to more efficient systems.
Step-by-step explanation:
The question pertains to the mechanical efficiency of gas turbines. Gas turbines have low mechanical efficiency because a significant portion of the power they generate is used to run the air compressor. Taking into account the provided references, it can be stated that for a gas turbine, about two-thirds (⅓) of the power output is required to run the air compressor. This is due to the large amount of energy needed to compress the air before the combustion process in the turbine cycle. Although not specified in the reference information given, this value of two-thirds is typically cited for gas turbines. For example, coal-fired power plants, which also involve turbines, convert about 40% of the input chemical energy into electricity, highlighting the substantial energy losses in thermal processes, as compared to the more efficient systems like electric motors where the conversion efficiency can exceed 90%.