Question

The intensity I of light bulb measured in watts per square meter (w/m^2), varies inversely as the square of the distance d from the light bulb . . suppose I is 45 w/m^2 when the distance is 5 m . find the intensity when the distance from the light bulb is 7 m away

Answer 1

I = k(1/d^2)
when I = 45, d = 5
45 = k/25
k =1125

so I = 1125/d^2

when d = 7
I = 1125/49 = appr 22.96

Answer 2

22.95918367