7.7 Radiation  (Page 7/13)

(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 $\text{34}\text{.}\text{0ºC}$ and has an emissivity of 0.970. The exposed area of skin is $0\text{.}\text{400}{\text{ m}}^2$ . 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 $\text{34}\text{.}\text{0ºC}$ . (b) Discuss how this situation would change if the sunlit side of the tent was nearly pure white and if the rider was covered by a white tunic.

Integrated Concepts

One $\text{30}\text{.}\text{0ºC}$ day the relative humidity is $\text{75}\text{.}\text{0\%}$ , and that evening the temperature drops to $\text{20}\text{.}\text{0ºC}$ , well below the dew point. (a) How many grams of water condense from each cubic meter of air? (b) How much heat transfer occurs by this condensation? (c) What temperature increase could this cause in dry air?

Integrated Concepts

Large meteors sometimes strike the Earth, converting most of their kinetic energy into thermal energy. (a) What is the kinetic energy of a ${\text{10}}^9\text{ kg}$ meteor moving at 25.0 km/s? (b) If this meteor lands in a deep ocean and $\text{80\%}$ of its kinetic energy goes into heating water, how many kilograms of water could it raise by $5\text{.}\text{0ºC?}$ (c) Discuss how the energy of the meteor is more likely to be deposited in the ocean and the likely effects of that energy.

Integrated Concepts

Frozen waste from airplane toilets has sometimes been accidentally ejected at high altitude. Ordinarily it breaks up and disperses over a large area, but sometimes it holds together and strikes the ground. Calculate the mass of $\text{0ºC}$ ice that can be melted by the conversion of kinetic and gravitational potential energy when a $\text{20}\text{.0 kg}$ piece of frozen waste is released at 12.0 km altitude while moving at 250 m/s and strikes the ground at 100 m/s (since less than 20.0 kg melts, a significant mess results).

Integrated Concepts

(a) A large electrical power facility produces 1600 MW of “waste heat,” which is dissipated to the environment in cooling towers by warming air flowing through the towers by $5\text{.}\text{00ºC}$ . What is the necessary flow rate of air in ${\text{m}}^3\text{/s}$ ? (b) Is your result consistent with the large cooling towers used by many large electrical power plants?