Astreet light is on top of a 9 foot pole. joe, who is 3 feet tall, walks away from the pole at a rate of 4 feet per second. at what speed is the tip of joe’s shadow moving from the base of the pole when he is 10 feet from the pole?

2 ft/s

Explanation:

Given

Length of Pole is 9 ft

Length of Joe is 3 ft

Joe walks away from Pole at the rate 4 ft/s

Let Joe is x m away from Pole so its shadow length is x'

From Similar triangle concept

3x'=x+x'

x=2x'

and it is given

Differentiating