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Nathan Moore 2023-01-08 13:17:50 -06:00
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@ -42,17 +42,29 @@ Planning to save money, one college student decides to go to an all-you-can-eat
Useful information: the student has a mass of 80kg and is made mostly of water. A Calorie heats 1 kg of water $1^{\circ}C$. Useful information: the student has a mass of 80kg and is made mostly of water. A Calorie heats 1 kg of water $1^{\circ}C$.
Answer Answer
\bea
3000kcals &=& 80kg\cdot1 \frac{kcal}{kg\cdot C^{\circ}}\cdot\Delta T\\
\Delta T &\approx& +37.5^{\circ}
\eea
Fat tissue serves a valuable purpose, brown fat, babies, songbirds Fat tissue serves a valuable purpose, brown fat, babies, songbirds
What power does the body give off in the more realistic case that the 3000kcal is burned over 24 hours? What power does the body give off in the more realistic case that the 3000kcal is burned over 24 hours?
Useful information: $1 kcal \approx 4200J$ and $1 J/s=1W$.
\be
\frac{3000kcal}{24hours}\frac{4200J}{1kcal}\frac{1hour}{3600sec}\approx145W
\ee
Survival swimming, putting all the kids in one bed on a cold winter night. Survival swimming, putting all the kids in one bed on a cold winter night.
Imagine that after eating a $600~kcal$ bacon maple long-john (donut), you decide to go for a hike to work off the Calories. Winona State is in a river valley bounded by 200m tall bluffs. How high up the bluff would you have to hike to burn off the donut? Imagine that after eating a $600~kcal$ bacon maple long-john (donut), you decide to go for a hike to work off the Calories. Winona State is in a river valley bounded by 200m tall bluffs. How high up the bluff would you have to hike to burn off the donut?
Useful information: human muscle is about $30\%$ efficient and gravitational energy on Earth's surface has a slope of about $10~Joules/kg\cdot m$. Useful information: human muscle is about $30\%$ efficient and gravitational energy on Earth's surface has a slope of about $10~Joules/kg\cdot m$.
Answer Answer
Energy bar charts
\bea
\frac{1}{3}\cdot600kcal\cdot\frac{4200J}{1kcal}
&=& 80kg\cdot10\frac{Joules}{kg\cdot m}\cdot height\\
height &\approx& 1000 m
\eea
increase in yields since 1917 (graph) increase in yields since 1917 (graph)
@ -65,7 +77,7 @@ Grow your own food, how far apart (urban life?)
\section{Example: How big could Tenochtitlan have been?} \section{Example: How big could Tenochtitlan have been?}
1917 (A&M) USDA pamphlet 1917 (A\&M) USDA pamphlet
Corn for US - area Corn for US - area