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.
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 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.
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?
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