Final answer:
The calculated efficiency of the thermal engine is approximately 44.44%, which doesn't match any of the provided options, suggesting a possible error in the question or the available choices.
Step-by-step explanation:
The efficiency of a thermal engine is calculated by the work output divided by the heat input. In this case, the engine produces 4 MJ (mega joules) of electrical energy (the work output), and it absorbs more than this amount since it also discards 5 MJ of heat to the cold temperature bath. To find the efficiency, we can use the formula:
Efficiency = (Work output / Heat input) x 100%
The heat input, in this case, also includes the 4 MJ of electrical energy output. The total heat absorbed is the sum of the work done (4 MJ) and the waste heat (5 MJ), which is 9 MJ. Now, using the numbers:
Efficiency = (4 MJ / 9 MJ) x 100% = (4/9) x 100% ≈ 44.44%
However, this efficiency is not one of the options provided, so it appears there is a mistake either in the question or in the interpretation of the available options. Considering the given options, this numerical discrepancy in the efficiency value is beyond what is expected for rounding errors or simplifications, which implies an error in the question or understanding the units of energy in the question.
Typically, engines are less than 100% efficient since some energy is always lost as waste heat. You would expect to choose an option less than 100%, but given none of the supplied options are close to the calculated efficiency, it would be best to clarify the question with the instructor.