SOLUTION: Please Help: The intensity of light (in foot-candle) varies inversely as the square of the distance (in feet) from the light source. The intensity of light 3 feet from the source

Question 1093805: Please Help: The intensity of light (in foot-candle) varies inversely as the square of the distance (in feet) from the light source. The intensity of light 3 feet from the source is 72 foot-candles. How far away is the source if the intensity of light is 2 foot-candles.
Thank you!
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
The intensity of light (in foot-candle) varies inversely as the square of the distance (in feet) from the light source.
The intensity of light 3 feet from the source is 72 foot-candles.
How far away is the source if the intensity of light is 2 foot-candles.
:
Intensity = k over distance
I = k/d^2
find k when I=72 and d=3
72 = k/3^2
72 = k/9
k = 9 * 72
k = 648
"How far away is the source if the intensity of light is 2 foot-candles?"
2 = 648/d^2
2d^2 = 648
divid2 both sides by 2
d^2 = 324
d =
d = 18 ft
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