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To sterilize a 50.0-g glass baby bottle, we must

raise its temperature from 22.0ºC to 95.0ºC . How much heat is transferred?

 

Rubbing your hands together warms them by converting work into thermal energy. If a woman rubs her hands back and forth for a total of 20 rubs, at a distance of 7.50 cm per rub, and with an average frictional force of 40.0 N, what is the temperature increase? The mass of tissues warmed is only 0.100 kg, mostly in the palms and fingers.

 

An ice bag containing 0°C ice is much more effective in absorbing heat than one containing the same amount of 0°C water.

a) How much heat is required to raise the temperature of 0.800 kg of water from 0°C to 30°C?

b) How much heat is required to first melt 0.800 kg of 0°C ice and then raise its temperature?

c) Explain how your answer supports the contention that the ice is more effective?

 

(a) Calculate the rate of heat conduction through house walls that are 13.0 cm thick and that have an average thermal conductivity twice that of glass wool. Assume there are no windows or doors. The surface area of the walls is 120 m2 and their inside surface is at 18.0ºC , while their outside surface is at 5.00ºC .

(b) How many 1-kW room heaters would be needed to balance the heat transfer due to conduction?

 

(a) Cherry-red embers in a fireplace are at 850ºC and have an exposed area of 0.200 m2 and an emissivity of 0.980. The surrounding room has a temperature of 18.0ºC. 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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