Work, Energy, and Power in Humans (Problem 47)

(a) What is the efficiency of an out-of-condition person who does $2.10\times {10}^5\text{ J}$ 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%? Select the answer to part (a).