1. Day 16, Physics 131, 2015

2. Asked about her school year, she replied: “Opa, it was not hard
Asked about her school year, she replied: “Opa, it was not hard. It is much easier when you read the [text]book.”
Katherine Alice Keller, June 26, 2015

3. HW Problem 17-7 In the morning, when the temperature is
286 K, a bicyclist finds that the absolute pressure in his tires in 501 kPa. That afternoon he find that the pressure in the tires has increased to 554 kPa.
? Ignoring expansion of the tires, find the afternoon temperature. ??

4. HW Problem 17-18
The air inside a hot-air balloon has an average temperature of 79.2oC. The outside air has a temperature of 20.3oC.
? What is the ratio of the density of air in the balloon to the density of air in the surrounding atmosphere ??

5. HW Problem 17-28
Three moles of oxygen gas (3.0 mol of O2) are placed in a portable container with a volume of m3. If the temperature of the gas is 295oC, find
? (a) the pressure of the gas ??
? (b) the average kinetic energy of an oxygen molecule ?
Suppose the volume of the gas is doubled, while the temperature and number of moles are held constant.
? By what factor do your answers in parts (a) and (b) change??

6. HW Problem 17-40
The deepest place in all the oceans is the Marianas Trench, were the depth is 10.9 km and the pressure is 1.1 x 108 Pa.
? If a copper ball 15.0 cm in diameter is taken to the bottom of the trench, by how much does its volume decrease ??

7. HW Problem 17-52 See the phase diagram for CO2.
? (a) What is the phase of CO2 at T = 20oC and P = 500 kPa ?
? (b) What is the phase of CO2 at T = -80oC and P = 120 kPa ?
? (c) What is the minimum pressure required to keep CO2 in the liquid phase at 20oC ?

8. HW Problem 17-71
A 48-g block of copper at -12oC is added to 110 g of water in a 75-g aluminum cup. The cup and the water have an initial temperature of 4.1oC.
? (a) find the equilibrium temperature of the cup and its contents ?
? (b) What mass of ice, if any, is present when the system reaches equilibrium ?

9. HW Problem 17-66
When you go out to your car one cold winter morning you discover a 0.58-cm-thick layer of ice on the windshield.
The windshield has an area of 1.5 m2.
The temperature of the ice is -2.0oC.
The density of the ice is 917 kg/m3.
? How much heat is required to melt all of the ice ??

10. HW Problem 18-52
During each cycle a reversible engine absorbs 2500 J of heat from a high-temperature reservoir and performs 2200 J of work.
(a) What is the efficiency of this engine ?
(b) How much heat is exhausted to the low-temperature reservoir during each cycle ?
(c) What is the ratio, Th/Tc of the two reservoir temperatures?

11. HW Problem 18-58
To keep a room at a comfortable 21.0oC, a Carnot heat pump does 345 J of work and supplies it with 3240 J of heat.
? (a) How much heat is removed from the outside air by the heat pump ?
? (b) What is the temperature of the outside air ?