A 48 kg woman cheats on her diet and eats a 439 Calorie (439 kcal) jelly donut f

Question

A 48 kg woman cheats on her diet and eats a 439 Calorie (439 kcal) jelly donut for breakfast. (a) How many joules of energy are the equivalent of one jelly doughnut? J (b) How many stairs must the woman climb to perform an amount of mechanical work equivalent to the food energy in one jelly doughnut? Assume the height of a single stair is 15 cm. stairs (c) If the human body is only 30% efficient in converting chemical energy to mechanical energy, how many stairs must the woman climb to work off her breakfast? stairs

Explanation / Answer

a) 1 calorie = 4.186 J

so 439 kcal = 439000 calorie = 439000 x 4.186 J = 1837654 J

b) Mechanical energy= potential energy = mgh

so mgh = input energy

mgh = 1837654 J

(48) (9.8) h = 1837654 J

h = 3906.58

height of one stair = 15 cm = 0.15 m

Total number of stairs = total height / height of one stair = 3906.58 / 0.15 = 26043.87

c) mechanical energy = 30% of chemical energy

mgh = 0.30 x 1837654 J

48 x 9.8 x h = 551296.2

h = 1171.97 m

height of one stair = 15 cm = 0.15 m

Total number of stairs = total height / height of one stair = 1171.97 m / 0.15 = 7813.13

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.