Daily Physicist

Today is the birthday of

• Katharine Burr Blodgett (1898-1979)
  
• Gordon Kidd Teal (1907-2003).

Today’s Problem: Gasoline equivalent of a jelly filled donut

If a jelly filled donut has 250 food calories (kcal), what is the energy equivalent of gasoline in milliliters, if a milliliter of gasoline contains 35 kJ of energy?

A food calorie is 1000 calories, and a calorie is 4.184 joules, so the joules per donut is:

\[\frac{250\;\mathrm{food calories}}{\mathrm{donut}}\left(\frac{1000\;\mathrm{calories}}{\mathrm{food calorie}}\right)\left(\frac{4.184\;\mathrm{J}}{\mathrm{calorie}}\right) = 1.05 \times 10^6\;\mathrm{J/donut}\]

Therefore the amount of gasoline containing \(1.05 \times 10^6\;\mathrm{J}\) is

\[1.05 \times 10^6\;\mathrm{J}\left(\frac{1.0\;\mathrm{mL}}{35 \times 10^3\;\mathrm{J}}\right) = 30\;\mathrm{mL} = 1.0\;\mathrm{oz}\]

So a 250 food calorie jelly filled donut has the energy equivalent of 30 mL or 1.0 oz of gasoline.