Hello, I\'m having trouble with problem 77 in College Physics8th Ed. I just don\

Question

Hello, I'm having trouble with problem 77 in College Physics8th Ed. I just don't know how to even begin. Here's theproblem: "In terms of saving energy, bicycling and walking are far moreefficient means of transportation than is travel byautomobile. For example, when riding at 10.0 mi/h, a cyclistuses food energy at a rate of about 400 kcal/h above what he woulduse 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 = 4186 J). Walking at 3.00mi/h requires about 220 kcal/h. It is interesting to comparethese values with the energy consumption required for travel bycar. Gasoline yields about 1.30 X J/gal. Find the fueleconomy in equivalent miles per gallon for a person (a) walking and(b) bicycling." As far as I understand it, the problem wants to convert kcal/hto J/gal, but I don't know how to convert hours to gallons (thekcal to J conversion is already given). I especially don'tknow how to use the equations of work, kinetic energy, andconservation of energy in this problem (which I suspect needs theseequations because that's what chapter 5 is all about). Thanksfor your help in advance! Hello, I'm having trouble with problem 77 in College Physics8th Ed. I just don't know how to even begin. Here's theproblem: "In terms of saving energy, bicycling and walking are far moreefficient means of transportation than is travel byautomobile. For example, when riding at 10.0 mi/h, a cyclistuses food energy at a rate of about 400 kcal/h above what he woulduse 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 = 4186 J). Walking at 3.00mi/h requires about 220 kcal/h. It is interesting to comparethese values with the energy consumption required for travel bycar. Gasoline yields about 1.30 X J/gal. Find the fueleconomy in equivalent miles per gallon for a person (a) walking and(b) bicycling." As far as I understand it, the problem wants to convert kcal/hto J/gal, but I don't know how to convert hours to gallons (thekcal to J conversion is already given). I especially don'tknow how to use the equations of work, kinetic energy, andconservation of energy in this problem (which I suspect needs theseequations because that's what chapter 5 is all about). Thanksfor your help in advance!

Explanation / Answer

Time taKen by the person to cover adistaance S byriding                       S/ v = t v = velocity of theperson. t = time he need to ride the bycle to cover a distance.
Energy consumed during by cycling             E = (400 kcal/h) (t in hrs) number of gallons require if thisenergy is delived by car            N = E [ (4186 J) / (1.30 J/gal)]
Simillarly walking the same distance Srequire energy E' ,                E ' = (220kcal /h) * [ S / (3mi/hr) ] number of gallons require ifthis energy is delived by car                  N'= E' * [ (4186 J) / (1.30 J/gal) ] .                    

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