In terms of saving energy, bicycling and walking are far more efficient means of

Question

In terms of saving energy, bicycling and walking are far more efficient means of transportation than is travel by automobile. For example, when riding at 14.0 mi/h, a cyclist uses food energy at a rate of about 400 kcal/h above what he would use if he were merely sitting still. (In exercise physiology, power is often measured in kcal/h rather than in watts. Here,

1 kcal = 1 nutritionist's Calorie = 4,186 J.)

Walking at 3.34 mi/h requires about 220 kcal/h. It is interesting to compare these values with the energy consumption required for travel by car. Gasoline yields about 1.30 108 J/gal.

(a) Find the fuel economy in equivalent miles per gallon for a person walking.
  . mpg

(b) Find the fuel economy in equivalent miles per gallon for a person bicycling.
mpg

Explanation / Answer

Amount of energy used per mile in cycling = 220 x 4186/3.34J/mi

for 1 gal 1.3 x 10^8 J is produced

so no miles with this enery is 1.3 x 10^8/(220 x 4186/3.34)

= 471.5 mi/gal

amount of energy used per mile in cycling = 400 x 4186/14J/mi

for 1 gal 1.3 x 10^8 J is produced

so no miles with this enery is 1.3 x 10^8/(400 x 4186/14)

= 1087 mi/gal

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