Question

Your favourite chocolate bar contains 1110 kJ of energy. If you go for a vigorous bike ride your metabolic rate will increase to 400 W. How long will you have to ride to use up the 1110 kJ from the chocolate bar (in minutes)?

Answer 1

By the definition of the power, we have:

$$P=\dfrac{W}{t},$$ $$t=\dfrac{1110\cdot10^3\ J}{400\ W}=2775\ s\cdot{1\ min}{60\ s}=46\ min.$$