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physics
thermodynamics
College Physics 7th edition Jerry D. Wilson, Anthony J. Buffa, Bo Lou - Solutions
Lead pellets of total mass 0.60 kg are heated to and then placed in a well-insulated aluminum cup of mass 0.20 kg that contains 0.50 kg of water initially at 17.3oC. What is the equilibrium temperature of the mixture?
A student mixes 1.0 L of water at 40oC with 1.0 L of ethyl alcohol at 20oC. Assuming that no heat is lost to the container or the surroundings, what is the final temperature of the mixture?
We all have had the experience that a room full of people always feels warmer than when the room is empty. Ten people are in a 4.0 m x 6.0 m x 3.0 m room at 20oC. If each person gives off heat at a rate of about 100 W and there is no heat loss to the outside of the room, what is the temperature of
How much heat is required to melt a 2.5-kg block of ice at 0oC?
How much heat is required to boil away 1.50 kg of water that is initially at 100oC?
(a) Converting 1.0 kg of water at 100oC to steam at 100oC requires (1) more heat, (2) the same amount of heat, (3) less heat than converting 1.0 kg of ice at to water at 0oC. Explain. (b) Calculate the difference in heat required to prove your answer to part (a).
Water is boiled to add moisture to the air in the winter to help a congested person breathe better. Calculate the heat required to boil away 1.0 L of water that is initially at 50oC.
An artist wants to melt some lead to make a statue. How much heat must be added to 0.75 kg of lead at 20oC to cause it to melt completely?
Atypical NBA basketball player will do about 3.00 x 106 J of work per hour. Express this work in Calories.
First calculate the heat that needs to be removed to convert 1.0 kg of steam at 100oC to water at 140oC and then compute the heat that needs to be removed to lower the temperature of water at 100oC to water at 40oC. Compare the two results. Are you surprised?
How much heat is required to completely boil away 0.50 L of liquid nitrogen at - 196oC? (Take the density of liquid nitrogen to be 0.80 x 103 kg/m3.)
An alcohol rub can rapidly decrease body (skin) temperature. (a) This is because of (1) the cooler temperature of the alcohol, (2) the evaporation of alcohol, (3) the high specific heat of the human body. (b) To decrease the body temperature of a 65-kg person by 1.0oC, what mass of alcohol must
Heat has to be removed to condense mercury vapor at a temperature of 630 K into liquid mercury. (a) This heat involves (1) only specific heat, (2) only latent heat, or (3) both specific and latent heats. Explain. (b) If the mass of the mercury vapor is 15 g, how much heat would have to be removed?
If 0.050 kg of ice at 0oC is added to 0.300 kg of water at 25oC in a 0.100-kg aluminum calorimeter cup, what is the final temperature of the water?
How much ice (at 0oC) must be added to 0.500 kg of water at 100 oC in a 0.200-kg aluminum calorimeter cup to end up with all liquid at 20 oC?
Ice (initially at 0 oC) is added to 0.75 L of tea at 20oC to make the coldest possible iced tea. If enough ice is added so the final mixture is all liquid, how much liquid is in the pitcher when this condition occurs?
To cool a very hot piece of 4.00-kg steel at 900 oC, the steel is put into a 5.00-kg water bath at 20 oC. What is the final temperature of the steel-water mixture?
Steam at is bubbled into 0.250 kg of water at in a calorimeter cup, where it condenses into liquid form. How much steam will have been added when the water in the cup reaches 60 oC? Ignore the effect of the cup.)
Evaporation of water from our skin is a very important mechanism for controlling body temperature. (a) This is because (1) water has a high specific heat, (2) water has a high latent heat of vaporization, (3) water contains more heat when hot, (4) water is a good heat conductor. (b) In a 3.5-h
Atypical person’s normal metabolic rate (the rate at which energy is consumed) is about 4 x 105 J/h, and the average food energy in a Big Mac is 600 Calories. If a person lived on nothing but Big Macs, how many per day would he or she have to eat to maintain a constant body weight?
A 0.400-kg piece of ice at – oC is placed in an equal mass of water at 30 oC. (a) When thermal equilibrium is reached between the two, (1) all the ice will melt, (2) some of the ice will melt, (3) none of the ice will melt. (b) How much ice melts?
One kilogram of a substance experimentally shows the T-versus-Q graph in Fig. 11.21.(a) What are its melting and boiling points? In SI units, what are (b) The specific heats of the substance during its various phases and (c) The latent heats of the substance at the various phase changes?
In an experiment, a 0.150-kg piece of a ceramic material at 20oC is placed in liquid nitrogen at its boiling point to cool in a perfectly insulated flask, which allows the gaseous N2 to immediately escape. How many liters of liquid nitrogen will be boiled away during this operation? (Take the
The single glass pane in a window has dimensions of 2.00 m by 1.50 m and is 4.00 mm thick. How much heat will flow through the glass in 1.00 h if there is a temperature difference of between the inner and outer surfaces? (Consider conduction only.)
Assume that a tile floor and an oak floor each have the same temperature and thickness. (a) Compared with the oak floor, the tile floor will conduct heat away from your bare feet (1) faster, (2) at the same rate, (3) slower. Why? (b) Calculate the ratio of the rate of heat flow of the tile floor
A house can have a brick wall or a concrete wall with the same thickness. (a) Compared with the concrete wall, the brick wall will conduct heat away from the house (1) faster, (2) at the same rate, (3) slower. Why? (b) Calculate the ratio of the rate of heat flow of the brick wall to that of the
Assume a goose has a 2.0-cm-thick layer of feather down (on average) and a body surface area of 0.15 m2. What is the rate of heat loss (conduction only) if the goose, with a body temperature of 41oC, is outside on a winter day when the air temperature is 11 oC?
Assume that your skin has an emissivity of 0.70, a nor-mal temperature of 34 oC, and a total exposed area of 0.25 m2. How much heat energy per second do you lose due to radiation if the outside temperature is 22 oC?
The U. S. five-cent coin, the nickel, has a mass of 5.1 g, a volume of 0.719 cm3, and a total surface area of 8.54 cm2. Assuming that a nickel is an ideal radiator, how much radiant energy per second comes from the nickel, if it is at 20oC?
An aluminum bar and a copper bar of identical cross-sectional area have the same temperature difference between their ends and conduct heat at the same rate. (a) The copper bar is (1) longer, (2) of the same length, (3) shorter than the aluminum bar. Why? (b) Calculate the ratio of the length of
A student ate a Thanksgiving dinner that totaled 2800 Cal. He wants to use up all that energy by lifting a 20-kg mass a distance of 1.0 m. Assume that he lifts the mass with constant velocity and no work is required in lowering the mass. (a) How many times must he lift the mass? (b) If he can
A copper teakettle has a circular bottom 30.0 cm in diameter that has a uniform thickness of 2.50 mm. It sits on a burner whose temperature is 150 oC. (a) If the teakettle is full of boiling water, what is the rate of heat conduction through its bottom? (b) Assuming that the heat from the burner
Assuming that the human body has a 1.0-cm-thick layer of skin tissue and a surface area of 1.5 m2, estimate the rate at which heat is conducted from inside the body to the surface if the skin temperature is 34 oC. (Assume a normal body temperature of 37oC for the temperature of the interior.)
The emissivity of an object is 0.50. (a) Compared with a perfect blackbody at the same temperature, this object would radiate (1) more power, (2) the same amount of power, (3) less power. Why? (b) Calculate the ratio of the power radiated by the blackbody to that radiated by the object.
A lamp filament radiates energy at a rate of 100 W when the temperature of the surroundings is 20oC, and only 99.5 W when the surroundings are at 30oC. If the temperature of the filament is the same in each case, what is its temperature in Celsius?
(a) If the Kelvin temperature of an object is doubled, its radiated power increases by (1) 2, (2) 4, (3) 8, (4) 16 times. Explain. (b) If its temperature is increased from 20oC to 40oC, by how much does the radiated power change?
A certain object with a surface temperature of 100oC is radiating heat at a rate of 200 J/s. To double the object’s rate of radiation energy, what should be its surface temperature in Celsius?
The thermal insulation used in building is commonly rated in terms of its R-value, defined as d/k, where d is the thickness of the insulation in inches and k is its thermal conductivity. In the United States, R-values are expressed in British units. For example, 3.0 in. of foam plastic would have
Apiece of pine 14 in. thick has an R-value of 19. (a) For glass wool to have the same R-value, its thickness should be (a) thicker than, (2) the same as, (3) thinner than 14 in. Why? (b) Calculate the required thickness of such a piece of glass wool.
Solar heating takes advantage of solar collectors such as the type shown in Fig. 11.22. During daylight hours, the average intensity of solar radiation at the top of the atmosphere is about 1400 W/m2. About of this radiation reaches the Earth during daylight hours. (The rest is reflected,
A large window measures 2.0 m by 3.0 m. At what rate will heat be conducted through the window when the room temperature is and the outside temperature is if (a) The window consists of a single pane of glass 4.0 mm thick and (b) The window instead has a double pane of glass (a “thermopane”),
It takes 2.0 x 106 J of heat to bring a quantity of water from to a boil. What is the mass of water?
The lowest natural temperature ever recorded on the Earth was at Vostok, a Russian Antarctic station, when a temperature of – 89.4 oC (–89.4oC) was recorded on July 21, 1983. Atypical person has a body temperature of, 37.0oC skin tissue 0.0250 m thick, and a total skin surface area of 1.50 m2.
The wall of a house is composed of a solid concrete block with an outside brick veneer and is faced on the inside with fiberboard, as illustrated in Fig. 11.23. If the outside temperature on a cold day is and the inside temperature is 20oC, how much energy is con-ducted through the wall in 1.0 h if
Suppose you wished to cut the heat loss through the wall in Exercise 61 in half by installing insulation. What thickness of Styrofoam should be placed between the fiberboard and concrete block to accomplish this goal?
A steel cylinder of radius 5.0 cm and length 4.0 cm is placed in end-to-end thermal contact with a copper cylinder of the same dimensions. If the free ends of the two cylinders are maintained at constant temperatures of 95oC (steel) and 15oC (copper), how much heat will flow through the cylinders
In Exercise 63, what is the temperature at the interface of the cylinders? In exercise A steel cylinder of radius 5.0 cm and length 4.0 cm is placed in end-to-end thermal contact with a copper cylinder of the same dimensions. If the free ends of the two cylinders are maintained at constant
A 0.60 kg piece of ice at 14oF is placed in 0.30 kg of water at 323 K. How much liquid is left when the system reaches thermal equilibrium?
A large Styrofoam cooler has a surface area of 1.0 m2 and a thickness of 2.5 cm. If 5.0 kg of ice at 0oC is stored inside and the outside temperature is a constant 35oC, how long does it take for all the ice to melt? (Consider conduction only.)
A 1600-kg automobile traveling at 55 mph brakes smoothly to a stop. Assume 40% of the heat generated in stopping the car is dissipated in the front steel brake disks. Each front disk has a mass of 3.0 kg. What is the temperature rise of the front brake disks during the stop?
A waterfall is 75 m high. If of the gravitational potential energy of the water went into heating the water, by how much would the temperature of the water, increase in going from the top of the falls to the bottom?
A 0.030-kg lead bullet hits a steel plate, both initially at 20oC. The bullet melts and splatters on impact. (This action has been photographed.) Assuming that of the bullet’s kinetic energy goes into increasing its temperature and then melting it, what is the minimum speed it must have to melt
The temperature of a lead block and a copper block, both 1.0 kg and at 20 oC, is to be raised to 100 oC. (a) The copper will require (1) more heat, (2) the same heat, (3) less heat than the lead. Why? (b) Calculate the difference between the heat required for the two blocks to prove your answer
A cyclist with a total skin area of 1.5 m2 is riding a bicycle on a day when the air temperature is 20oC and her skin temperature is 34oC. The cyclist does work at about 200 W (moving the pedals) but her efficiency is only about in terms of converting energy into mechanical work. Estimate the
A 200-kg cast iron machine part at 500oC is left to cool at room temperature. Assume the machine part is a cube and has an emissivity of 0.780. At what rate is the machine part initially losing heat due to radiation?
A 5.00-g pellet of aluminum reaches a final temperature of 63 oC when gaining 200 J of heat. What is its initial temperature?
Blood can carry excess heat from the interior to the surface of the body, where the heat is transferred to the outside environment. If 0.250 kg of blood at a temperature of 37.0 oC flows to the surface and loses 1500 J of heat, what is the temperature of the blood when it flows back into the
Explain why the process shown in Fig. 12.1b is not that for an ideal gas at constant temperature.
If ideal gas sample A receives more heat than ideal gas sample B, will sample A experience a higher increase in internal energy? Explain.
Does the entropy of each of the following objects increase or decrease? (a) Ice as it melts; (b) Water vapor as it condenses; (c) Water as it is heated on a stove; (d) Food as it is cooled in a refrigerator.
A student challenges the second law of thermodynamics by saying that entropy does not have to increase in all situations, such as when water freezes to ice. Is this challenge valid? Why or why not?
A student tries to cool his dormitory room by opening the refrigerator door. Will that work? Explain.
If heat engine A absorbs more heat than heat engine B from a hot reservoir, will engine A necessarily do more net work than engine B? Explain your reasoning.
The maximum efficiency of a heat engine is 1 (or). Can the COP of a thermal pump be greater than 1? Explain.
Diesel engines are more efficient than gasoline engines. Which type of engine wold you expect to run hotter? Why?
On a p–V diagram, sketch a cyclic process that consists of an isothermal expansion followed by an isobaric compression, and lastly followed by an isometric process.
In Fig. 12.19, the plunger of a syringe is pushed in quickly, and the small pieces of paper in the syringe catch fire. Explain this phenomenon using the first law of thermodynamics. (Similarly, in a diesel engine, there are no spark plugs. How can the air€“ fuel mixture ignite?)
In an isobaric process, an ideal gas sample can do work on the environment but its temperature also increases. How can this be?
An ideal gas initially at temperature To, pressure po, and volume Vo is compressed to one-half its initial volume. As shown in Fig. 12.20, process 1 is adiabatic, 2 is isothermal, and 3 is isobaric. Rank the work done on the gas and the final temperatures of the gas, from highest to lowest, for all
While playing in a tennis match, you lost 6.5 x 105 of heat, and your internal energy also decreased by 1.2 x 106J. How much work did you do in the match?
A fixed quantity of gas undergoes the reversible changes illustrated in the p€“V diagram in Fig. 12.22. How much work is done in each process?
Suppose that after the final process in Fig. 12.22 (Exercise 10), the pressure of the gas is decreased isometrically from 1.0 x 105 Pa to 0.70 x 105Pa, and then the gas is compressed isobarically from 1.0 m3 to 0.80 m3. What is the total work done in all of these processes, including 1 through 5?In
A gas is enclosed in a cylindrical piston with a 12.0-cm radius. Heat is slowly added to the gas while the pressure is maintained at 1.00 atm. During the process, the piston moves 6.00 cm. (a) This is an (1) isothermal, (2) isobaric, (3) adiabatic process. Explain. (b) If the heat transferred to
2.0 mol of an ideal gas expands isothermally from a volume of 20 L to 40 L at 20 oC. (a) The work done by the gas is (1) positive, (2) negative, (3) zero. Explain. (b) What is the magnitude of the work?
A monatomic ideal gas (y = 1.67) is compressed adiabatically from a pressure of 1.00 x 105Pa and volume of 240 L to a volume of 40.0 L. (a) What is the final pressure of the gas? (b) How much work is done on the gas?
An ideal gas sample expands isothermally by tripling its volume and doing 5.0 x 104J of work at 40 oC. (a) How many moles of gas are there in the sample? (b) Was heat added to or removed from the sample, and how much?
The temperature of 2.0 mol of ideal gas is increased from 150 oC to 250 oC by two different processes. In process A, 2500 J of heat is added to the gas; in process B, 3000 J of heat is added. (a) In which case is more work done: (1) process A, (2) process B, or (3) the same amount of work is done?
One handred moles of a monatomic gas is com-pressed as shown on the p€“V diagram in Fig. 12.23.(a) Is the work done by the gas (1) positive, (2) zero, or (3) negative? Why? (b) What is the work done by the gas? (c) What is the change in temperature of the gas? (d) What is the change in
One mole of an ideal gas is taken through the cyclic process shown in Fig. 12.24.(a) Compute the work involved for each of the four processes. (b) Find ˆ†U, W, and Q for the complete cycle. (c) What is T3?
What is the change in entropy of mercury vapor (Lv = 2.7 x 105 J/kg) when 0.50 kg of it condenses to a liquid at its boiling point of 357 oC?
A rigid container contains 1.0 mol of an ideal gas that slowly receives 2.0 x 104J of heat. (a) The work done by the gas is (1) positive, (2) zero, (3) negative. Why? (b) What is the change in the internal energy of the gas?
2.0 kg of ice melts completely into liquid water at 0 oC. (a) The change in entropy of the ice (water) in this process is (1) positive, (2) zero, (3) negative. Explain. (b) What is the change in entropy of the ice (water)?
A process involves 1.0 kg of steam condensing to water at 100 oC. (a) The change in entropy of the steam (water) is (1) positive, (2) zero, (3) negative. Why? (b) What is the change in entropy of the steam (water)?
During a liquid-to-solid phase change of a substance, its change in entropy is – 4.19 x 103 J/K. If 1.67 x 106 J of heat is removed in the process, what is the freezing point of the substance in degrees Celsius?
In an isothermal expansion at 27 oC, an ideal gas does 60 J of work. What is the change in entropy of the gas?
One mole of an ideal gas undergoes an isothermal compression at 0 oC, and 7.5 x 103 J of work is done in compressing the gas. (a) Will the entropy of the gas (1) increase, (2) remain the same, or (3) decrease? Why? (b) What is the change in entropy of the gas?
A quantity of an ideal gas undergoes an isothermal expansion at 20 oC and does 3.0 x 103 J of work on its surroundings in the process. (a) Will the entropy of the gas (1) increase, (2) remain the same, or (3) decrease? Explain. (b) What is the change in the entropy of the gas?
In the winter, heat from a house with an inside temperature of 18 oC leaks out at a rate of 2.0 x 104 J. The out-side temperature is 0 oC. (a) What is the change in entropy per second of the house? (b) What is the total change in entropy per second of the house–outside system?
An isolated system consists of two very large thermal reservoirs at constant temperatures of 100 oC and 0 oC. Assume the reservoirs made contact and 1000 J of heat flew from the cold reservoir to the hot reservoir spontaneously. (a) The total change in entropy of the isolated system (both
Two large heat reservoirs at temperatures 200 oC and 60 oC, respectively, are brought into thermal contact, and 1.50 x 103J of heat spontaneously flows from one to the other with no significant temperature change. (a) The change in the entropy of the two-reservoir system is (1) positive, (2) zero,
A system goes from state 1 to state 3 as shown on the T€“S diagram in Fig. 12.25.(a) The heat transfer for the process going from state 2 to state 3 is (1) positive, (2) zero, (3) negative. Explain. (b) Calculate the total heat transferred in going from state 1 to state 3.
A quantity of ideal gas goes through an isothermal process and does 400 J of net work. (a) The internal energy of the gas is (1) higher than, (2) the same as, (3) less than when it started. Why? (b) Is a net amount of heat added to or removed from the system, and how much is involved?
Suppose that the system described by the T–S diagram in Fig. 12.25 is returned to its original state, state 1, by a reversible process depicted by a straight line from state 3 to state 1. (a) The change in entropy of the system for this overall cyclic process is (1) positive, (2) zero, (3)
A 50.0-g ice cube at oC is placed in 500mL of water at 20 oC. Estimate the change in entropy (after all the ice has melted) (a) For the ice, (b) For the water, and (c) For the ice–water system.
If an engine does 200 J of net work and exhausts 800 J of heat per cycle, what is its thermal efficiency?
A gasoline engine has a thermal efficiency of 28%. If the engine absorbs 2000 J of heat per cycle, (a) What is the net work output per cycle? (b) How much heat is exhausted per cycle?
A heat engine with a thermal efficiency of does 500 J of net work each cycle. How much heat per cycle is lost to the low-temperature reservoir?
An internal combustion engine with a thermal efficiency of 15.0% absorbs 1.75 * 105 J absorbs of heat from the hot reservoir. How much heat is lost by the engine in each cycle?
The heat output of a particular engine is 7.5 x 103J per cycle, and the net work out is 4.0 x 103 J per cycle. (a) The heat input is (1) less than 4.0 x 103 J, (2) between and 4.0 x 103 J and 7.5 x 103 J, (3) greater than 7.5 x 103 J. Explain. (b) What is the heat input and thermal efficiency of
A gasoline engine burns fuel that releases 3.3 x 108 J of heat per hour. (a) What is the energy input during a 2.0-h period? (b) If the engine delivers 25 kW of power during this time, what is its thermal efficiency?
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