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Chapter 14: Q3CQ (page 500)
When heat transfers into a system, is the energy stored as heat? Explain briefly.
The energy stored during heat can also be different forms of energy rather than heat alone.
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(a) Calculate the rate of heat transfer by radiation from a car radiator at 110掳C into a 50.0潞C environment, if the radiator has an emissivity of 0.750 and a\({\bf{1}}{\bf{.20}}\;{{\bf{m}}^{\bf{2}}}\)surface area. (b) Is this a significant fraction of the heat transfer by an automobile engine? To answer this, assume a horsepower of 200 hp (1.5 kW) and the efficiency of automobile engines as 25%.
The brakes in a car increase in temperature by\({\bf{\Delta T}}\)when bringing the car to rest from a speed\(v\). How much greater would\({\bf{\Delta T}}\)be if the car initially had twice the speed? You may assume the car to stop sufficiently fast so that no heat transfers out of the brakes.
What is the temperature of ice right after it is formed by freezing water?
The Sun radiates like a perfect black body with an emissivity of exactly 1. (a) Calculate the surface temperature of the Sun, given that it is a sphere with a\({\bf{7}}{\bf{.00 \times 1}}{{\bf{0}}^{\bf{8}}}\;{\bf{m}}\)radius that radiates\({\bf{3}}{\bf{.80 \times 1}}{{\bf{0}}^{{\bf{26}}}}{\bf{ W}}\)into 3-K space. (b) How much power does the Sun radiate per square meter of its surface? (c) How much power in watts per square meter is that value at the distance of Earth,\({\bf{1}}{\bf{.50 \times 1}}{{\bf{0}}^{{\bf{11}}}}{\bf{ m}}\)away? (This number is called the solar constant.)
(a) Cherry-red embers in a fireplace are at 850潞C and have an exposed area of\({\bf{0}}{\bf{.200}}\;{{\bf{m}}^{\bf{2}}}\)and an emissivity of 0.980. The surrounding room has a temperature of 18.0潞C. If 50% of the radiant energy enters the room, what is the net rate of radiant heat transfer in kilowatts? (b) Does your answer support the contention that most of the heat transfer into a room by a fireplace comes from infrared radiation?
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