thermodynamics

1. On a hot summer day, a student accidentally leaves his dorm room refrigerator open, and on, 

when he leaves his room in the morning. The dorm is well insulated, but not air conditioned; all 

of the doors and windows are closed.

a. Draw a simple picture of the room after the student leaves it showing all significant mass 

and energy flows into and out of the room. 

b. When the student returns to his room in the evening, will the room be warmer or cooler

than the vacant neighboring dorm room? Why?

2. A wind turbine – with a rotor diameter of roughly 80 m – is located in Bowling Green, Ohio, 

where the average, steady wind speed is about 6.5 m/s. Determine the mechanical energy of the 

air per unit mass, and find the power generation potential of the wind turbine. Assume the air 

density to be 1.25 kg/m3

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3. The cold cranking amperes (CCA) of a conventional lead-acid automobile battery is the amount 

of current the battery can provide at 0°F for 30 seconds and maintain at least 1.2 volts per cell (or 

7.2 volts for a standard 12-volt battery). If a battery is rated for 700 CCA, how much work will it 

deliver to the starter motor, assuming the minimum voltage (7.2 V) and maximum time (30 s) are 

required?

4. The central HVAC unit for Kettering Labs goes down over the summer, and the class in KL221

wishes to install window mounted air-conditioning units having 18,000 Btu/hr cooling capacity. 

The classroom contains 43 people with an average resting heat dissipation rate of about 325 kJ/h

per person. There are 10 lights in the room, each with a rating of 100 W. The rate of heat transfer 

to the classroom through the walls and the windows is estimated to be 15,000 kJ/h. If the room air 

is to be maintained at a constant temperature of 21°C, how many window air-conditioning units 

are required?