Question

A 52 kg woman cheats on her diet and eats a 540 kcal jelly donut for breakfast. (a) How many joules of energy are the equivalent of one jelly doughnut? (b) How many stairs must the woman climb to perform an amount of mechanical work equivalent to the food energy in one jelly doughnut?

Answer 1

Answer:

a)801KJoules

b)The woman must climb stairs for an equivalent of 1.57km

Number of stairs=7850 stairs

Explanation:

a)We use the conversion between Joules and Kcal:

4184Joules=1Kcal

540Kcal*(1484Joules/1Kcal)=801KJoules

b)The physical Work must be equal to the food energy

$W_{physical}=E_{food}\\ mgh=E_{food}\\h=E_{food}/(mg)=801KJoules/(52Kg*9.81m/s^{2})=1.57Km$

The woman must climb stairs for an equivalent of 1.57Km

For example if an stair measure 20cm=0.2m

Number of stairs=1.57km/0.2m=7850 stairs