Question

The resistance of an exercise bike is often provided by a generator; that is, the energy that you expend is used to generate electric energy, which is then dissipated. Rather than dissipate the energy, it could be used for practical purposes.
a. A typical person can maintain a steady energy expenditure of 400 W on a bicycle. Assuming a typical efficiency for the body, and a generator that is 80% efficient, what useful electric power could you produce with a bicycle-powered generator?

b. How many people would need to ride bicycle generators simultaneously to power a 400 W TV in the gym?

Answer 1

a. Typical efficiency of human body = 25%

So, useful electric power will be,

P = (Energy)*(Typical efficiency of human body)*(Typical efficiency of generator)

P = 400*(25/100)*(80/100)

P = 80 W

b.

Let 'n' number of people need to produce 400 W power.

From above part,

Useful power produced by one person = 80 W

So, (number of people)*(Useful power produced by one person) = 400

n*80 = 400

n = 400/80

n = 5

therefore 5 people would need to ride bicycle generators simultaneously to power a 400 W TV in the gym.

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