BIO Internal energy change while biking you set your station

BIO Internal energy change while biking you set your stationary bike on a high 80-N friction-like resistive force and cycle for 30 min at a speed of 8.0 m/s. Your body is 10% efficient at converting chemical energy in your body into mechanical work, (a) what is your internal chemical energy change? (b) How long must you bike to convert 3.0 times 10^5 J of chemical potential while staying at this speed? (This amount of energy equals the energy released by the body after eating three slices of bread.)

Solution

the change in internal chemical energy :

    E =W/n = f.s/n = f*v*t / n = 80*8*30*60 / (10/100) = 11.52x10⁶ = 11.52 MJ

The time t is calculated as follows:

    t = En/fv = 3x10⁵*(10/100) /80*8 = 46.875 s = 46.9 s = 0.78 min