In physics, a light source of luminous intensity K candelas is said to have Illu

Question

In physics, a light source of luminous intensity K candelas is said to have Illuminance I = K/s^2 on a flat surface s ft away. Suppose a small, unshaded lamp of luminous intensity 35 candelas is connected to a rope that allows it to be raised and lowered between the floor and the top of a 22-ft-high coiling. Assume that the lamp is being raised and lowered in such a way that at time t (in min) it is s = 9t - t^2 ft above the floor. (a) Express the illuminance on the floor as a composite function of f for 0

Explanation / Answer

I=K l s2

s=9t -t2

a. I(t)=K l(9t-t2)2

b. at t=4

I(5)=35 *22(9*4 - 42)2=308000

c. at t=7

I(7)=35*22(9*7 -72)2=150920

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