A street light is at the top of a 11 ft. tall pole. A man 6.2 ft tall walks away from the pole with a speed of 4.5 feet/sec along a straight path. How fast is the tip of his shadow moving when he is 31 feet from the pole?

Answer 1

x = distance man from pole
y = distance tip of shadow from pole

(y-x)/6.2 = y/11
11(y-x) = 6.2 y
4.8 y = 11 x
y = 2.29 x

dy/dt = 2.29 dx/dt = 2.29 * 4.5 = 10.3ft/s