Suppose a lot of papers are strewn all over the floor; then you stack them neatly. Does this violate the second law of thermodynamics? Explain.

A heat engine does $7200$ $\mathrm{J}$ of work in each cycle while absorbing $12.0$ kcal of heat from a high-temperature reservoir. What is the efficiency of this engine?

Think up several processes (other than those already mentioned) that would obey the first law of thermodynamics, but, if they actually occurred, would violate the second law.

Calculate the largest permissible value of P for the beam and loading shown, knowing that the allowable normal stress is +6 ksi in tension and -18 ksi in compression.

A particular car does work at the rate of about $7.0 \mathrm{~kJ} / \mathrm{s}$ when traveling at a steady $20.0 \mathrm{~m} / \mathrm{s}$ along a level road. This is the work done against friction. The car can travel $17 \mathrm{~km}$ on $1 \mathrm{~L}$ of gasoline at this speed (about $40 \mathrm{mi} / \mathrm{gal}$ ). What is the minimum value for $T_{\mathrm{H}}$ if $T_{\mathrm{L}}$ is $25^{\circ} \mathrm{C}$ ? The energy available from $1 \mathrm{~L}$ of gas is $3.2 \times 10^7 \mathrm{~J}$.

A heat engine does 9200 J of work per cycle while absorbing 22.0 kcal of heat from a high-temperature reservoir. What is the efficiency of this engine?

A person decides to lose weight by sleeping one hour less per day, using the time for light activity. How much weight (or mass) can this person expect to lose in $1$ year, assuming no change in food intake? Assume that $1$ $kg of fat stores about$9000$ kcal of energy.

A heat engine produces $8200$ $\mathrm{J}$ of heat while performing $3200$ $\mathrm{J}$ of useful work. What is the efficiency of this engine?

Make up an ad for a car engine that violates the second law of thermodynamics.

Use the conservation of energy to explain why the temperature of a well-insulated gas increases when it is compressed-say, by pushing down on a piston-whereas the temperature decreases when the gas expands. Show your reasoning.

Assume that a $65\text{-}\mathrm{kg}$ hiker needs to eat $4.0 \times 10^3 \mathrm{kcal}$ of energy to supply a day's worth of metabolism $\left(=Q_H\right)$. Estimate the elevation change the person can climb in one day, using only this amount of energy. As a fun and rough prediction, treat the person as an isolated heat engine, operating between the internal temperature of $37^{\circ} \mathrm{C}\left(98.6^{\circ} \mathrm{F}\right)$ and the ambient air temperature of $20^{\circ} \mathrm{C}$.

Why is a foam cup used in a student calorimeter rather than a typical glass beaker?

The COPs are defined differently for heat pumps and air conditioners. Explain why.

A heat engine exhausts 8200 J of heat while performing 3200 J of useful work. What is the efficiency of this engine?