Pave It Over Suppose city 1 leaves an entire block (100 m × 100 m) as a park with trees and grass (emissivity 0.96) while city 2 paves the same area over with asphalt (emissivity 1.0). Sunlight heats each surface to 40.0 °C by sunset, and then the surface radiates its heat into a cube of air 100 m on a side and at 30.0 °C. (a) At what rate does the park in city 1 deliver energy to the air at sunset? (b) At what rate does the asphalt in city 2 deliver energy to the air at sunset? (c) If each city block maintains the same radiated power for 2.0 h and there are no other energy losses, what are the final temperatures of the cubes of air above each city block? The density of air at 30.0 °C is 1.16kg/m 3 . Although this example is oversimplified, a more sophisticated analysis recently showed that a city park can cool the air that passes through it by more than 4 °C.
Pave It Over Suppose city 1 leaves an entire block (100 m × 100 m) as a park with trees and grass (emissivity 0.96) while city 2 paves the same area over with asphalt (emissivity 1.0). Sunlight heats each surface to 40.0 °C by sunset, and then the surface radiates its heat into a cube of air 100 m on a side and at 30.0 °C. (a) At what rate does the park in city 1 deliver energy to the air at sunset? (b) At what rate does the asphalt in city 2 deliver energy to the air at sunset? (c) If each city block maintains the same radiated power for 2.0 h and there are no other energy losses, what are the final temperatures of the cubes of air above each city block? The density of air at 30.0 °C is 1.16kg/m 3 . Although this example is oversimplified, a more sophisticated analysis recently showed that a city park can cool the air that passes through it by more than 4 °C.
Pave It Over Suppose city 1 leaves an entire block (100 m × 100 m) as a park with trees and grass (emissivity 0.96) while city 2 paves the same area over with asphalt (emissivity 1.0). Sunlight heats each surface to 40.0 °C by sunset, and then the surface radiates its heat into a cube of air 100 m on a side and at 30.0 °C. (a) At what rate does the park in city 1 deliver energy to the air at sunset? (b) At what rate does the asphalt in city 2 deliver energy to the air at sunset? (c) If each city block maintains the same radiated power for 2.0 h and there are no other energy losses, what are the final temperatures of the cubes of air above each city block? The density of air at 30.0 °C is 1.16kg/m3. Although this example is oversimplified, a more sophisticated analysis recently showed that a city park can cool the air that passes through it by more than 4 °C.
Study of body parts and their functions. In this combined field of study, anatomy refers to studying the body structure of organisms, whereas physiology refers to their function.
A Thermopane window of area 5 m² is con-
structed of two layers of glass, each 4.4 mm
thick separated by an air space of 3 mm.
If the inside is at 11°C and the outside is
at -24°C, what is the heat loss through the
window? The thermal conductivity of glass is
0.8 W/m .° C and of air is 0.0234 W/m .° C.
Answer in units of kW.
Seals may cool themselves by using thermal windows, patches on their bodies with much higher than average surface temperature. Suppose a seal has a 0.030 m2 thermal window at a temperature of 30°C. If the seal’s surroundings are a frosty -10°C, what is the net rate of energy loss by radiation? Assume an emissivity equal to that of a human.
A sphere of radius 0.50 m, temperature 27.0 °C, and emissivity 0.850 is located in an environment of temperature 77.0 °C. At what rate does the sphere
emit thermal radiation?
absorb thermal radiation?
What is the sphere’s net rate of energy exchange?
Chapter 16 Solutions
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