A 68 kg bike rider rides a bike for half an hour. (Cycling at 15km/hr = Metaboli

Question

A 68 kg bike rider rides a bike for half an hour. (Cycling at 15km/hr = Metabolic power (W) of 480)

a)

How much energy (in joules) has the rider used as an energy input?

b)

Assuming the human body has an efficiency of 25%, how much energy actually went towards moving

the bike

? (this is the useful energy output)

c)

The cyclist is someone who drinks Coke and is trying to lose weight. One Coke contains 140 Calories.

How many joules of energy is in one can of Coke?

d)

How many cans of Coke does this half hour bike ride “burn”?

Explanation / Answer

(A) P = 480 W

t = 3600/2 = 1800 sec

Energy = P t = 8.64 x 10^5 J

(B) Eout = (8.64 x 10^5)(0.25)

= 2.16 x 10^5 J

(C) E0 = 140 x 4.186 = 586.04 J

(if it is 140 kcal then E0 = 586040 J )

(D) n = Ein / E0 = 1474 can

(if that was in kilocaloie then 1.5 can)

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