A bicyclist consumes 9.0 L of water over the span of 3.5...

A bicyclist consumes 9.0 L of water over the span of 3.5 hours during a race. Making the approximation that 80$\%$ of the cyclist's energy goes into evaporating this water (at 20$^\circ$C)
as sweat, how much energy in kcal did the rider use during the ride? [$Hint$: See page 399.]

Key Concepts

Latent Heat of Vaporization

This concept refers to the energy required to convert a specific mass of a substance from its liquid phase to its vapor phase at a given temperature without a change in temperature. In the context of the problem, it explains how much energy is needed to evaporate the water (sweat) produced during exercise.

Energy Partitioning in Biological Systems

In biological contexts, the energy obtained from metabolism is distributed among various physiological processes. Here, the fact that 80% of the cyclist’s total metabolic energy is used in the evaporation process of sweat is a prime example of how energy is partitioned to maintain homeostasis during strenuous activity.

Mass-Volume Conversion

This is the process of converting a given volume of a substance into its corresponding mass using the density of the substance. Since water has a density of approximately 1 kg per liter, this conversion simplifies calculations by allowing volume measurements to be directly treated as mass, which is essential when applying energy per unit mass.

Unit Conversion in Energy Calculations

Converting between units, such as from Joules or calories to kilocalories, is crucial in energy calculations. Understanding and applying these conversions ensures that the final answer is expressed in the correct units, making the energy expenditure understandable and comparable in real-life contexts.

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