Question

On a very tough hill, a mountain biker puts out an impressive 376W of power. Assume his body's efficiency for converting chemical to mechanical energy is 20%.

a) At what rate is he burning food energy,in Calories per hour?

b) What is his oxygen uptake rate VO,in liters per minute?

Answer 1

a) The mechanical energy output of the person's body is given to be

Po = 376 W

His power converting efficientcy is given to be 20%

So, the power consumed by him is given by

So,

Now, 1 watt = 0.24 calories/second

So,

1880 W = 1880*0.24 = 451.2 calories/second

So, the calories burnt per hour is

Ptot = 451.2*3600 = 1624320 calories/ hour

b) For 5 calorie of energy burnt, the human body takes in approximately 1 liter of oxygen.

In one minute, the calories burnt is

P = 451.2*60 = 27072 calorie

So, oxygen intake = 27072*1/5 = 5414.4 liters/minute