Subtopic: Sources of power on the farm – human, animal, mechanical, electrical, wind, solar and biomass
Question Statement:
An agricultural worker operating a rotary pedal thresher works at a metabolic energy expenditure rate of $24.0\text{ kJ/min}$. If the human mechanical work efficiency is $20\%$ ($0.20$), the sustained mechanical power output delivered by the worker in Watts is ________ (answer in integer).
Answer Key:
80
Step-by-Step Solution & Explanation
1. Metabolic power expenditure ($P_{met}$):
$P_{met} = \frac{24.0\text{ kJ/min} \times 1000\text{ J/kJ}}{60\text{ s}} = 400\text{ W}$
2. Mechanical power output ($P_{mech}$):
$P_{mech} = P_{met} \times \eta_{mech} = 400\text{ W} \times 0.20 = 80\text{ W}$
(Note: An average adult agricultural laborer can sustain approximately $0.1\text{ hp} \approx 75\text{ W}$ of continuous mechanical power).