SOLUTION: The intensity of light​ (in foot-candles) varies inversely as the square of​ x, the distance in feet from the light source. The intensity of light 2 feet from the sourc

Algebra ->  Customizable Word Problem Solvers  -> Misc -> SOLUTION: The intensity of light​ (in foot-candles) varies inversely as the square of​ x, the distance in feet from the light source. The intensity of light 2 feet from the sourc      Log On

Ad: Over 600 Algebra Word Problems at edhelper.com


    

Question 1072077: The intensity of light​ (in foot-candles) varies inversely as the square of​ x, the distance in feet from the light source. The intensity of light 2 feet from the source is 20 ​foot-candles. How far away is the source if the intensity of light is 5 ​foot-candles?
Answer by rothauserc(4718) About Me  (Show Source):
You can put this solution on YOUR website!
let k be the constant of proportionality, then
:
I = k / x^2
:
we are given I = 20 and x = 2, then
:
20 = k / 2^2
:
k = 80
:
for I = 5, we have
:
5 = 80 / x^2
:
x^2 = 80 / 5 = 16
:
x = square root(16) = 4
:
*************************
The source is 4 feet away
*************************
: