Multiple ChoiceA cubic Styrofoam cooler containing ice on a hot day is shown in the following figure. The thickness of each wall of the cooler is 15 mm, with a side length of 1 m. If it is 40°C outside, how long will 2 kg of ice last in the cooler? Assume that during the melting process, the temperature inside the cooler remains at 0°C and that no heat enters from the bottom of the cooler. Note that the latent heat of fusion for water is 334 kJ/kg and the thermal conductivity of Styrofoam is 0.033 W/mK.612views3rank2comments
Multiple ChoiceIf the intensity of sunlight measured at the Earth's surface is 1400 W/m2 , what is the surface temperature of the Sun? Treat the Sun like a true blackbody. Note that the distance from the Earth to the Sun is 1.5 x 1011 m and the radius of the Sun is 696 million meters.518views1comments
Multiple Choice450J of work are done on a gas in a process which decreases the thermal energy by 200J. How much heat energy is transferred to or from the system?331views
Multiple Choice300g of water at 40°C is in an insulated cup. What mass of copper at 500°C must be added to heat the water to 60°C?347views
Multiple ChoiceA rigid container holds 12g of O2 gas at 30°C. How much energy must be added to the gas to bring its temperature to 50°C?304views
Textbook QuestionThe blood plays an important role in removing heat from the body by bringing this energy directly to the surface where it can radiate away. Nevertheless, this heat must still travel through the skin before it can radiate away. Assume that the blood is brought to the bottom layer of skin at 37.0°C and that the outer surface of the skin is at 30.0°C. Skin varies in thickness from 0.50 mm to a few millimeters on the palms and soles, so assume an average thickness of 0.75 mm. A 165-lb, 6-ft-tall person has a surface area of about 2.0 m2 and loses heat at a net rate of 75 W while resting. On the basis of our assumptions, what is the thermal conductivity of this person's skin?662views
Textbook QuestionTwo rods, one made of brass and the other made of copper, are joined end to end. The length of the brass section is 0.300 m and the length of the copper section is 0.800 m. Each segment has cross-sectional area 0.00500 m^2 . The free end of the brass segment is in boiling water and the free end of the copper segment is in an ice–water mixture, in both cases under normal atmospheric pressure. The sides of the rods are insulated so there is no heat loss to the surroundings. (b) What mass of ice is melted in 5.00 min by the heat conducted by the composite rod?1558views1rank
Textbook QuestionThe emissivity of tungsten is 0.350. A tungsten sphere with radius 1.50 cm is suspended within a large evacuated enclosure whose walls are at 290.0 K. What power input is required to maintain the sphere at 3000.0 K if heat conduction along the supports is ignored?941views
Textbook QuestionA spherical pot contains 0.75 L of hot coffee (essentially water) at an initial temperature of 95°C. The pot has an emissivity of 0.60, and the surroundings are at 20.0°C. Calculate the coffee's rate of heat loss by radiation.1163views1comments
Textbook QuestionAn electric kitchen range has a total wall area of 1.40 m^2 and is insulated with a layer of fiberglass 4.00 cm thick. The inside surface of the fiberglass has a temperature of 175°C, and its outside surface is at 35.0°C. The fiberglass has a thermal conductivity of 0.040 W/m K. (a) What is the heat current through the insulation, assuming it may be treated as a flat slab with an area of 1.40 m^2 ?2956views
Textbook QuestionSuppose that the rod in Fig. 17.24a is made of copper, is 45.0 cm long, and has a cross-sectional area of 1.25 cm^2 . Let TH = 100.0°C and TC = 0.0°C. (a) What is the final steady-state temperature gradient along the rod? 631views
Textbook QuestionA carpenter builds an exterior house wall with a layer of wood 3.0 cm thick on the outside and a layer of Styrofoam insulation 2.2 cm thick on the inside wall surface. The wood has k = 0.080 W/m K, and the Styrofoam has k = 0.027 W/m K. The interior surface temperature is 19.0°C, and the exterior surface temperature is -10.0°C. (a) What is the temperature at the plane where the wood meets the Styrofoam?174views
Textbook QuestionA carpenter builds an exterior house wall with a layer of wood 3.0 cm thick on the outside and a layer of Styrofoam insulation 2.2 cm thick on the inside wall surface. The wood has k = 0.080 W/m K, and the Styrofoam has k = 0.027 W/m K. The interior surface temperature is 19.0°C, and the exterior surface temperature is -10.0°C. (b) What is the rate of heat flow per square meter through this wall?117views
Textbook QuestionMost stars are main-sequence stars, a group of stars for which size, mass, surface temperature, and radiated power are closely related. The sun, for instance, is a yellow main-sequence star with a surface temperature of 5800 K. For a main-sequence star whose mass M is more than twice that of the sun, the total radiated power, relative to the sun, is approximately P/Pₛᵤₙ=1.5(M/Mₛᵤₙ)^3.5 . The star Regulus A is a bluish main-sequence star with mass 3.8Mₛᵤₙ and radius 3.1Rₛᵤₙ. What is the surface temperature of Regulus A?542views
Textbook QuestionLiquid helium, with a boiling point of 4.2 K, is used in ultralow-temperature experiments and also for cooling the superconducting magnets used in MRI imaging in medicine. Storing liquid helium so far below room temperature is a challenge because even a small 'heat leak' will boil the helium away. A standard helium dewar, shown in FIGURE P19.67, has an inner stainless-steel cylinder filled with liquid helium surrounded by an outer cylindrical shell filled with liquid nitrogen at –196°C. The space between is a vacuum. The small structural supports have very low thermal conductivity, so you can assume that radiation is the only heat transfer between the helium and its surroundings. Suppose the helium cylinder is 16 cm in diameter and 30 cm tall and that all walls have an emissivity of 0.25. The density of liquid helium is 125 kg/m^3 and its heat of vaporization is 2.1×10^4 J/kg. a. What is the mass of helium in the filled cylinder?650views1rank
Textbook QuestionYou are boiling pasta and absentmindedly grab a copper stirring spoon rather than your wooden spoon. The copper spoon has a 20 mm ×1.5 mm rectangular cross section, and the distance from the boiling water to your 35°C hand is 18 cm. How long does it take the spoon to transfer 25 J of energy to your hand?332views
Textbook QuestionThe ends of a 20-cm-long, 2.0-cm-diameter rod are maintained at 0°C and 100°C by immersion in an ice-water bath and boiling water. Heat is conducted through the rod at 4.5×10^4 J per hour. Of what material is the rod made?496views
Textbook QuestionA 2.0-cm-diameter metal sphere is glowing red, but a spectrum shows that its emission spectrum peaks at an infrared wavelength of 2.0 μm. How much power does the sphere radiate? Assume e=1 .187views
Textbook QuestionA ceramic cube 3.0 cm on each side radiates heat at 630 W. At what wavelength, in μm, does its emission spectrum peak? Assume e=1.184views
Textbook QuestionA house has a volume of 1200 m³ .(a) What is the total mass of air inside the house at 15°C?117views
Textbook Question(I) To what temperature will 6800 J of heat raise 3.0 kg of water that is initially at 10.0°C?121views
Textbook Question(II) A small immersion heater is rated at 375 W. Estimate how long it will take to heat a cup of soup (assume this is 250 mL of water) from 15°C to 75°C.135views
Textbook Question(I) One end of a 64-cm-long copper rod with a diameter of 2.0 cm is kept at 460°C, and the other is immersed in water at 22°C. Calculate the heat conduction rate along the rod.109views
Textbook QuestionThe temperature within the Earth’s crust increases about 1.0 C° for each 30 m of depth. The thermal conductivity of the crust is 0.80 J/s C° .(a) Determine the heat transferred from the interior to the surface for the entire Earth in 1.0 h.177views
Textbook QuestionA leaf of area 40cm² and mass 4.5 x 10⁻⁴ kg directly faces the Sun on a clear day. The leaf has an emissivity of 0.85 and a specific heat of 0.80 kcal/kg · K .(a) Estimate the energy absorbed per second by the leaf from the Sun, and then130views
Textbook Question(II) Heat conduction to skin. Suppose 150 W of heat flows by conduction from the blood capillaries beneath the skin to the body’s surface area of 1.5 m² . If the temperature difference is 0.50 C°, estimate the average distance of capillaries below the skin surface.147views
Textbook Question(II) When a diver jumps into the ocean, water leaks into the gap region between the diver’s skin and her wetsuit, forming a water layer about 0.5 mm thick. Assuming the total surface area of the wetsuit covering the diver is about 1.0m² , and that ocean water enters the suit at 10°C and is warmed by the diver to skin temperature of 35°C, estimate how much energy (in units of candy bars = 300kcal ) is required by this heating process.139views
Textbook Question(I) (a) How much power is radiated by a tungsten sphere (emissivity e = 0.35) of radius 19 cm at a temperature of 25°C? (b) If the sphere is enclosed in a room whose walls are kept at - 5 °C, what is the net flow rate of energy out of the sphere?162views
Textbook Question(II) A copper rod and an aluminum rod of the same length and cross-sectional area are attached end to end (Fig. 19–35). The copper end is placed in a furnace maintained at a constant temperature of 205°C. The aluminum end is placed in an ice bath held at a constant temperature of 0.0°C. Calculate the temperature at the point where the two rods are joined.<IMAGE>206views
Textbook Question(a) Estimate the total power radiated into space by the Sun, assuming it to be a perfect emitter at T = 5500 K. The Sun’s radius is 7.0 x 10⁸ m. (b) From this, determine the power per unit area arriving at the Earth, 1.5 x 10¹¹ m away (Fig. 19–37).<IMAGE>155views
Textbook QuestionA 12-g lead bullet traveling at 220 m/s passes through a thin wall and emerges at a speed of 160 m/s. If the bullet absorbs 50% of the heat generated,(b) If the bullet’s initial temperature was 20°C, will any of the bullet melt, and if so, how much?124views
Textbook QuestionIn a cold environment, a person can lose heat by conduction and radiation at a rate of about 200 W. Estimate how long it would take for the body temperature to drop from 36.6°C to 35.6°C if metabolism were nearly to stop. Assume a mass of 65 kg. (See Table 19–1.)<IMAGE>138views
Textbook QuestionA leaf of area 40cm² and mass 4.5 x 10⁻⁴ kg directly faces the Sun on a clear day. The leaf has an emissivity of 0.85 and a specific heat of 0.80 kcal/kg · K . (b) estimate the rate of rise of the leaf’s temperature.133views
Textbook QuestionA mountain climber wears a goose-down jacket 3.8 cm thick with total surface area 0.95 m² . The temperature at the surface of the clothing is -18°C and at the skin is 34°C. Determine the rate of heat flow by conduction through the jacket assuming (a) it is dry and the thermal conductivity k is that of goose down, and (b) the jacket is wet, so k is that of water and the jacket has matted to 0.50 cm thickness.125views
Textbook QuestionEstimate the rate at which heat can be conducted from the interior of the body to the surface. As a model, assume that the thickness of tissue is 4.0 cm, that the skin is at 34°C and the interior at 37°C, and that the surface area is 1.5m² . Compare this to the measured value of about 230 W that must be dissipated by a person working lightly. This clearly shows the necessity of convective cooling by the blood.145views
Textbook QuestionA leaf of area 40cm² and mass 4.5 x 10⁻⁴ kg directly faces the Sun on a clear day. The leaf has an emissivity of 0.85 and a specific heat of 0.80 kcal/kg · K .(c) Will the temperature rise continue for hours? Why or why not?143views
Textbook QuestionThe temperature within the Earth’s crust increases about 1.0 C° for each 30 m of depth. The thermal conductivity of the crust is 0.80 J/s C° .(b) Compare this heat to the 1000 W/m² that reaches the Earth’s surface in 1.0 h from the Sun.105views
Textbook Question(a) Using the solar constant, estimate the rate at which the whole Earth receives energy from the Sun. (b) Assume the Earth radiates an equal amount back into space (that is, the Earth is in equilibrium). Then, assuming the Earth is a perfect emitter, ( e = 1.0) estimate its average surface temperature. [Hint: Discuss why you use area A = πr²_E or A = 4πr²_E in each part.]142views
Textbook QuestionApproximately how long should it take 8.2 kg of ice at 0°C to melt when it is placed in a carefully sealed Styrofoam ice chest of dimensions 25cm x 35cm x 55cm whose walls are 1.5 cm thick? Assume that the conductivity of Styrofoam is double that of air and that the outside temperature is 34°C.124views
Textbook Question(II) A ceramic teapot ( e = 0.70) and a shiny metal one ( e = 0.10) each hold 0.55 L of tea at 85°C. (a) Estimate the rate of heat loss from each, and (b) estimate the temperature drop after 30 min for each. Consider only radiation, and assume the surroundings are at 20°C.22views
Textbook Question(II) How long does it take the Sun to melt a block of ice at 0°C with a flat horizontal area 1.0 m² and thickness 1.0 cm? Assume that the Sun’s rays make an angle of 35° with the vertical and that the emissivity of ice is 0.050.43views
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