A street light is at the top of a 14 ft tall pole. A woman 6 ft tall walks away from the pole with a speed of 7 ft/sec along a straight path. How fast is the tip of her shadow moving when she is 45 ft from the base of the pole?

Answer 1

Using similar triangles, the distance s of the shadow's tip when she is x ft from the pole, is
(s-x)/6 = s/14
s = 7/4 x
ds/dt = 7/4 dx/dt
Check my math, and then plug in your numbers.
Note that the speed does not depend on her distance x