A 55-kg woman cheats on her diet and eats a 465-Calorie (465 kcal) jelly doughnut for breakfast.

(c) If the human body is only 24% efficient in converting chemical energy to mechanical energy, how many stairs must the woman climb to work off her breakfast?

I got 24075.32468 stairs to perform an amount of mechanical work equivalent to the food in one jelly doughnut (which is correct). I assumed that I would just multiply that number by 0.76 (100%-24%) and then add my answer to 24075 stairs, but that was wrong. I then tried the 24% but that was wrong to. What do I do?

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To determine how many stairs the woman must climb to work off her breakfast, you need to consider the energy conversion efficiency factor of 24%. Here's how you can calculate the correct number of stairs:

1. Calculate the energy content of the jelly doughnut in kilocalories (kcal):
Energy content of the jelly doughnut = 465 kcal

2. Convert the energy content to kilojoules (kJ) since the unit of work is usually measured in joules:
Energy content in kilojoules = 465 kcal * 4.184 kJ/kcal
= 1939.56 kJ

3. Determine the amount of mechanical work needed to climb one stair. This can vary depending on various factors such as the height and depth of each stair, but for simplicity, let's assume it takes an average of 0.25 kJ of work to climb a stair.

4. Divide the energy content of the jelly doughnut by the work required to climb one stair:
Stairs to climb = Energy content in kilojoules / Work required per stair
= 1939.56 kJ / 0.25 kJ
= 7758.24 stairs

5. As you mentioned, the human body is only 24% efficient in converting chemical energy to mechanical energy. Therefore, you need to adjust the calculated number of stairs by multiplying it by the efficiency factor:
Effective stairs to climb = Stairs to climb / Efficiency factor
= 7758.24 stairs / 0.24
= 32326 stairs (rounded to the nearest whole number)

So, the woman would need to climb approximately 32,326 stairs to work off the energy from one jelly doughnut, accounting for the 24% efficiency of energy conversion in the human body.