Question

An average person expends about 845 kilojoules of energy per hour of walking. Suppose a person eats 2 baked potatoes with butter, each having 37 grams of carbohydrates and 4.3 grams of protein from the potato and 4 grams of fat from the butter. How many hours of walking will it take for the person to expend the energy from the two potatoes?

Answer 1

Answer:

         $\large\boxed{2hours}$

Explanation:

You will need to use the conversion between food calories, calories and joules.

       $1\text { nutritional calorie }= 1,000cal\\ \\ 1cal=4.184joule$

From a nutritional table (from the internet) you can obtain the amount of nutritional calories for each type macronutrient: carbohydrates, protein, and fat.

Macronutrient      food calories

Carbohydrate         4 cal/g

Protein                    4 cal/g

Fat                           9 cal/g

To convert food calories to regular calories, mutiply by the conversion factor:

                $1=1,000cal/\text{nutritional calorie}$

Macronutrient        calories

Carbohydrate         4,000 cal/g

Protein                    4,000 cal/g

Fat                           9,000 cal/g

To convert regular calories to joules, multiply by the conversion factor:

               $1=4.184 joule/1cal$

Macronutrient        energy in joules

Carbohydrate         16,736 joule/g

Protein                    16,736 joule/g

Fat                           37,656 joule/g

Now you can multiply the grams of each macronutrient in one potato by its energy content:

Macronutrient        energy/gram     ×   grams  =  total energy

Carbohydrate         16,736 joule/g   ×   37 g      =  619,232 joules

Protein                    16,736 joule/g   ×   4.3 g     =  71,968.8 joules

Fat                           37,656 joule/g  ×   4 g        = 150,624 joules

Total = 619,232 joules + 71,968.8 joules + 150,624 joules = 841,820.8 joules.

Since they are two potatoes, multiply by 2: × 841,820.8 joules = 1,683,641.6 joules.

Divide by 1,000 to convert to kilojoules = 1,683.64 kilojoules

Divide the total energy from the two potatoes by the energy that an average person expend per hour of walking (845 kilojoules of energy per hour):

       $1,683.64kilojoules/845kilojouesl/hour=1.99hours\approx 2hours$