As he cycles at a constant speed on level ground, at what rate is chemical energy being converted to thermal energy in his body, assuming a typical efficiency of \(25 \%\) for the conversion of chemical energy to the mechanical energy of motion?

A. \(480 \mathrm{~W}\)

B. \(360 \mathrm{~W}\)

C. \(240 \mathrm{~W}\)

D. \(120 \mathrm{~W}\)

A \(68 \mathrm{~kg}\) cyclist is pedaling down the road at \(15 \mathrm{~km} / \mathrm{h}\), using a total metabolic power of \(480 \mathrm{~W}\). A certain fraction of this energy is used to move the bicycle forward, but the balance ends up as thermal energy in his body, which he must get rid of to keep cool. On a very warm day, conduction, convection, and radiation transfer little energy, and so he does this by perspiring, with the evaporation of water taking away the excess thermal energy.