(a) What is the efficiency of an out-of-condition professor...

(a) What is the efficiency of an out-of-condition professor who does $2.10 \times 10^{5} \mathrm{J}$ of useful work while metabolizing 500 kcal of food energy? (b) How many food calories would a well-conditioned athlete metabolize in doing the same work with an efficiency of $20 \% ?$

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Key Concepts

Energy Conversion Efficiency

This concept refers to the ratio of the useful work output to the total energy input, often expressed as a percentage. It is a critical parameter in understanding how effectively a system or organism converts energy from one form (such as metabolic energy from food) into mechanical work. In biological contexts, it helps explain differences in performance or productivity between individuals or systems.

Unit Conversion Between Food Calories and Joules

Food energy is typically measured in kilocalories (kcal), but energy in physics is often expressed in Joules. Understanding the conversion is essential since 1 kilocalorie (kcal) is equivalent to approximately 4184 Joules. This conversion allows for a consistent comparison and calculation when relating energy input from food to mechanical work output.

Metabolic Energy and Mechanical Work

This concept involves the transformation of chemical energy stored in food into mechanical work performed by the body. It highlights the idea that only a fraction of the energy consumed is converted to useful work, with the remainder largely lost as heat. The efficiency of this conversion is crucial in fields such as physiology and bioenergetics, where energy balance and performance are analyzed.

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