Final answer:
If our bodies were able to use gasoline with 20% efficiency, we could pedal a bicycle at 15 km/h for approximately 1083.3 kilometers on the energy contained in 1 gallon of gasoline.
Step-by-step explanation:
To estimate how far you could pedal a bicycle on the energy contained in 1.0 gallon of gasoline, we consider the energy content of the gasoline and the efficiency of a human bicycling. One gallon of gasoline contains approximately 130 megajoules (MJ) of energy. The average person cycling at a moderate effort level may be about 20% efficient at converting food energy to mechanical energy. For simplicity, we'll assume that if our bodies could use gasoline, we'd also be 20% efficient with it.
The energy used by a cyclist pedal at 15 km/h is far less than the energy content of 1 gallon of gasoline. If we assume that biking at 15 km/h requires roughly 100 watts of power, this translates to 0.1 kilowatts. Therefore, to find out how long the 130 MJ of gasoline could last, we convert it to kilowatt-hours (kWh), where 1 MJ equals 0.2778 kWh. This gives us approximately 36.11 kWh for the energy in 1.0 gallon of gasoline.
If our bodies were 20% efficient, we'd effectively use 0.2 x 36.11 = 7.222 kWh of that energy. Since power is energy over time, and we want to know the time, we rearrange the equation for time, giving us time = energy/power. This amounts to 7.222 kWh / 0.1 kW, which equals 72.22 hours of cycling. Finally, by multiplying the cycling time by the speed, i.e., 72.22 hours x 15 km/h, we find that one could pedal 1083.3 kilometers on the energy content of 1 gallon of gasoline when cycling at 15 km/h.