(a) What is the average metabolic rate in watts of a man who...

(a) What is the average metabolic rate in watts of a man who metabolizes $10,500 \mathrm{kJ}$ of food energy in one day? (b) What is the maximum amount of work in joules he can do without breaking down fat, assuming a maximum efficiency of $20.0 \% ?(\mathrm{c})$ Compare his work output with the daily output of a 187-W (0.250-horsepower) motor.

Key Concepts

Metabolic Rate and Power

Metabolic rate measured in watts is an expression of the average power output required to sustain a biological process over time. It is calculated by converting the total energy consumed (in joules) over a given period (in seconds), which provides insight into the average rate of energy expenditure. This concept is central to understanding how energy intake relates to the work a system can perform.

Energy Unit Conversion

Converting between different energy units, such as kilojoules to joules, is essential in both physics and biology because it allows for consistent use of SI units in calculations. Establishing the correct conversion factor ensures accurate determination of energy over time, which is crucial when deriving quantities like power.

Efficiency in Energy Conversion

Efficiency is the ratio of useful work output to the total energy input, expressed as a percentage or decimal fraction. In biological systems, efficiency indicates how much of the metabolized energy can be converted into mechanical work, highlighting the inherent losses in energy conversion processes. This concept is pivotal when estimating the maximum work output from a given energy source.

Comparison of Work Outputs

Comparing work outputs involves converting energy or power values into comparable units, such as joules or watts, to assess the performance of different systems. By evaluating the daily energy output of a biological system against that of a mechanical device, one can understand relative efficiencies and the scaling of power in various contexts.

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