Question

An athlete is 18% efficient performing a specific exercise. They eat an apple,
which delivers 490 kcal to their body. For how many minutes must they exercise,
generating mechanical energy at a rate of 200 W, to “burn off” the calories contained in
the apple?

Answer 1

$$\eta E=Pt\\0.18(490\cdot 4184)=200t\\t=1845\ s=30.75\ min$$