A light is hung 15 ft above a straight horizontal path. If a man 6 ft tall is walking away from the light at the rate of 5 ft/sec, how fast is his shadow lengthening and at what rate is the tip of the man’s shadow moving?

Answer 1

depends on where the man is.

If the man's distance is x, and the shadow has length s, then

(x+s)/15 = s/6

Now just differentiate and plug in the distance when you finally deign to include it.

Answer 2

If the man is 8 feet away from the light?