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TLeo198
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Homework Statement
After filtering through the atmosphere, the Sun's radiation illuminates Earth's surface with an average intensity of 1.0 kW/m^2. Assuming this radiation strikes the 15-m x 45-m black, flat roof of a building at normal incidence, calculate the average force the radiation exerts on the roof.
Homework Equations
Dunno if this is all I need, but;
(1)I-average = u-average (energy density) x c (speed of light) = P-average (power) / A (area)
(2)P-average = F-average (force) x d (distance), where d = c (speed of light) x t (time), where time is 500 seconds, since that's how long it takes for light to reach the Earth from the sun.
The Attempt at a Solution
Since it's asking for average force, I remembered that P = Fxd. I knew I could find P-average by setting the intensity equal to P/A, in which A = 15m x 45m = 675 m^2, therefore getting a P-average of 675,000 Watts. I then went to the equation P = F x d, found d to be (c)(t) = (3 x 10^8)(500s) = 1.5 x 10^11 meters. Plugging that in, I calculated the average force to be about 4.5 x 10^-6 Newtons, but that answer does not coincide with the correct answer in the back of the book. Any comments? Any help is greatly appreciated