he power of sunlight reaching each square meter of the Earth\'s surface on a cle
ID: 2153063 • Letter: H
Question
he power of sunlight reaching each square meter of the Earth's surface on a clear day in the tropics is close to 1 000 W. On a winter day in Manitoba, the power concentration of sunlight can be 100 W/m2. Many human activities are described by a power per unit area on the order of 102 W/m2 or less.(a) Consider, for example, a family of four paying $66 to the electric company every 30 days for 654 kWh of energy carried by electrical transmission to their house, which has floor dimensions of 13.0 m by 9.50 m. Compute the power per unit area used by the family.
W/m2
(b) Consider a car 2.01 m wide and 4.90 m long traveling at 55.0 mi/h using gasoline having "heat of combustion" 44.0 MJ/kg with fuel economy 25.0 mi/gal. One gallon of gasoline has a mass of 2.54 kg. Find the power per unit area used by the car.
W/m2
Explanation / Answer
Every month $66 for 30 days at 654 kWh==>area is 13*9.5=123.5 m2
30 days*X=654 kWh==>654/(24 hours*30 days)0.9083 kW or 908.3 W
a) 908.3/(13*9.5)7.355 W/m2= power per unit area 7.355 W/m2
b) 55 miles per hour/25 gallons2.2 gallons==>2.54 kg*2.2 gallons=5.588 kg
44 Mj/kg*5.588 kg245.96 Mj per hour/360068333 W/(2.01*4.9)6938.1 W/m2
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