A regulation NFL football field, including its end zones, is exactly 120 yards l

Question

A regulation NFL football field, including its end zones, is exactly 120 yards long and 160 feet wide. At noon on a certain cloudless day, the Sun is shining on the field with an intensity of 825 W/m2. The albedo of the field is 0.550. (a) What is the downward force of sunlight on the field? (b) A newly minted half-dollar coin weighs 11.340 g. Which force is greater: that exerted by the light pressure on a football field, or the weight of two half dollars still sitting on it after several coin tosses by a clumsy referee?

Explanation / Answer

first 120 yards = 109.73 meters 160 yards = 146.30 meters

So area of field = 109.73 * 146.30 = 16054 m^2

force = pressure * area = [ (1+albedo) * intensity / c ] * area =

= (1.550 * 825 / 3x10^8) * 16054 =

= 0.0466 Newtons (answer to part a)

weight of two coins = mg = (2 * 0.011340) * 9.8 = 0.222 Newtons weight of coins is greater

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