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Consider a person outdoors on a cold night. Construct a problem in which you calculate the rate of
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Tutorials in Introductory Physics
- Thermography is a technique for measuring radiant heat and detecting variations in surface temperatures that may be medically, environmentally, or militarily meaningful.(a) What is the percent increase in the rate of heat transfer by radiation from a given area at a temperature of 34.0C compared with that at 33.0C, such as on a person’s skin? (b) What is the percent increase in the rate of heat transfer by radiation from a given area at a temperature of 34.0C compared with that at 20.0C, such as for warm and cool automobile hoods? Figure 14.35 Artist’s rendition of a thermograph of a patient’s upper body, showing the distribution of heat represented by different colors.arrow_forward(a) It is difficult to extinguish a fire on a crude oil tanker, because each liter of crude oil releases 2.80107J of energy when burned. To illustrate this difficulty, calculate the number of liters of water that must be expended to absorb the energy released by burning 1.00 L of crude oil, it the water has its temperature raised from 20.0C to 100C, it boils, and the resulting steam is raised to 300C. (b) Discuss additional complications caused by the fact that crude oil has a smaller density than water.arrow_forwardCalculate the rate of heat conduction out of the human body, assuming that the core internal temperature is 37.0C, the skin temperature is 34.0C, the thickness of the tissues between averages 1.00 cm, and the surface area is 1.40m2.arrow_forward
- For the human body, what is the rate of heat transfer by conduction through the body’s tissue with the following conditions: the tissue thickness is 3.00 cm, the change in temperature is 2.00C, and the skin area is 1.50m2. How does this compare with the average heat transfer rate to the body resulting from an energy intake of about 2400 kcal per day? (No exercise is included.)arrow_forwardA firewalker runs across a bed of hot coals without sustaining burns. Calculate the heat transferred by conduction into the sole of one foot of a firewalker given that the bottom of the foot is a 3.00-mm-thick callus with a conductivity at the low end of the range for wood and its density is 300 kg/m3. The area of contact is 25.0 cm2 the temperature of the coals is 700 , and the time in contact is 1.00 s. Ignore the evaporative cooling of sweat.arrow_forwardEven when shut down after a period of normal use, a large commercial nuclear reactor transfers thermal energy at the rate of 150 MW by the radioactive decay of fission products. This heat transfer causes a rapid increase in temperature it the cooling system fails (1 watt 2 1 joule/second or 1W=1J/s and 1MW=1megawatt ). (a) Calculate the rate of temperature increase in degrees Celsius per second (C/s) if the mass of the reactor core is 1.60105kg and it has an average specific heat of 0.3349kJ/kgC. (b) How long would it take to obtain a temperature increase of 2000C, which could cause some metals holding the radioactive materials to melt? (The initial rate of temperature increase would be greater than that calculated here because the heat transfer is concentrated in a smaller mass. Later, however, the temperature increase would slow down because the 5105-kg steel containment vessel would also begin to heat up.) Figure 14.32 Radioactive spentfuel pool at a nuclear power plant. Spent fuel stays hot for a long time. (credit: U.S. Department of Energy)arrow_forward
- How can an object transfer heat if the object does not possess a discrete quantity of heat?arrow_forward(a) A shirtless rider under a circus tent feels the heat radiating from the sunlit portion of the tent. Calculate the temperature of the tent canvas based on the following information: The shirtless rider’s skin temperature is 34.0C and has an emissivity of 0.970. The exposed area of skin is 0.400m2. He receives radiation at the rate of 20.0 W—half what you would calculate if the entire region behind him was hot. The rest of the surroundings are at 34.0C. (b) Discuss how this situation would change if the sun lit side of the tent was nearly pure white and if the rider was covered by a white tunic.arrow_forward(a) How much heat transfer is necessary to raise the temperature of a 0.200kg piece of ice from 20.0C to 130C, including the energy needed for phase changes? (b) How much time is required for each stage, assuming a constant 20.0kJ/s rate of heat transfer? (c) Make a graph of temperature versus time for this process.arrow_forward
- (a) A firewalker runs across a bed of hot coals without sustaining burns. Calculate the heat transferred by conduction into the sole of one foot of a firewalker given that the bottom of the foot is a 3.00-mm-thick callus with a conductivity at the low end of the range for wood and its density is 300kg/m3. The area of contact is 25.0cm2, the temperature of the coals is 700C, and the time in contact is 1.00 s. (b) What temperature increase is produced in the 25.0cm3 of tissue affected? (c) What effect do you think this will have on the tissue, keeping in mind that a callus is made of dead cells?arrow_forwardA person inhales and exhales 2.00 L of 37.0C air, evaporating 4.00102g of water from the lungs and breathing passages with each breath. (a) How much heat transfer occurs due to evaporation in each breath? (b) What is the rate of heat transfer in watts if the person is breathing at a moderate rate of 18.0 breaths per minute? (c) If the inhaled air had a temperature of 20.0C, what is the rate of heat transfer for warming the air? (d) Discuss the total rate of heat transfer as it relates to typical metabolic rates. Will this breathing be a major form of heat transfer for this person?arrow_forward(a) What is the rate of heat conduction through the 3.00-cm-thick fur of a large animal having a I .40-m surface area? Assume that the animal's skin temperature is 32.0 , that the air temperature is 5.00 , and that has the same thermal conductivity as air. (b) What food intake will the animal need in one day to replace this heat transfer?arrow_forward
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