A52 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?

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

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

62.5%

Explanation:

Efficiency of a machine is expressed as;

Efficiency = Work output/Work input * 100%

work input is the quantity of heat transferred to the engine

Work output is the heat transferred to the surrounding.

Given

Work input = 40.0kJ

Work output = 25.0kJ

Get the efficiency of the engine;

Efficiency = 25/40 * 100

Efficiency = 5/8 * 100

Efficiency = 500/8

Efficiency = 62.5%

Hence the efficiency (in percent) of the cyclical heat engine is 62.5%