SOLUTION: The intensity I of light from a light bulb varies inversely as the square of the distance d from the light bulb. Suppose I is 640 w/m^2 when the distance is 8m. How much farther wo

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Question 336858: The intensity I of light from a light bulb varies inversely as the square of the distance d from the light bulb. Suppose I is 640 w/m^2 when the distance is 8m. How much farther would it be to a point where the intensity is 90 w/m^2?
Answer by Alan3354(69443) About Me  (Show Source):
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The intensity I of light from a light bulb varies inversely as the square of the distance d from the light bulb. Suppose I is 640 w/m^2 when the distance is 8m. How much farther would it be to a point where the intensity is 90 w/m^2?
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I+=+k%2Fd%5E2 k is a constant, d = distance
640 = k/8^2 = k/64
k = 40960
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For 90 w/m^2:
90 = 40960/d^2
d^2 = 40960/90
d = 64/3 meters