The useful power output of Bryan Allen, who flew a human-powered airplane across the English Channel on June 12th, 1979, was about 350 W. The propellor of the airplane was driven by the pilot's legs, using a bicycle-tyoed mechanism. Using the efficiency for legs (20%), calculate the food energy he needed for the 2.5-hour trip.

foodenergy*.25=350*timeinseconds

so figure the time in seconds in 2.5hrs

Your answer will be in joules. To get Food calories,

foodcalories=energyinjoules/4200 joules

62.5

To calculate the food energy needed for the 2.5-hour trip, we will first determine the amount of work done by Bryan Allen based on his power output of 350 W and the duration of the flight.

Work (in joules) is calculated as the product of power (in watts) and time (in seconds):

Work = Power × Time

Since the time is given as 2.5 hours, we need to convert it to seconds:

Time = 2.5 hours × 60 minutes/hour × 60 seconds/minute

Time = 9,000 seconds

Now we can calculate the work done:

Work = 350 W × 9,000 seconds

Work = 3,150,000 joules

However, the given power output of 350 W represents the useful power output, taking into account the efficiency of the legs (20%). So, the total work done by the legs would be:

Total Work = Useful Power ÷ Efficiency

Total Work = 350 W ÷ 0.20

Total Work = 1,750 joules

Now, considering the energy efficiency of the human body, which is typically around 20% to 25%, we can find the food energy needed by the pilot. We use an efficiency of 20% in this calculation:

Food Energy = Total Work ÷ Efficiency

Food Energy = 1,750 joules ÷ 0.20

Food Energy = 8,750 joules

Therefore, the food energy Bryan Allen needed for the 2.5-hour trip was 8,750 joules.