A light is atop a 16-ft pole. A 5-ft tall boy walks away from the pole at the rate of 4 ft/sec. At what rate is the tip of his shadow moving when he is 18 feet from the pole? At what rate is the length of his shadow increasing? Please show your work.

Question

A light is atop a 16-ft pole.  A 5-ft tall boy walks away from the pole at the rate of 4 ft/sec.  At what rate is the tip of his shadow moving when he is 18 feet from the pole?  At what rate is the length of his shadow increasing?  Please show your work.

anonymous · Answer

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Take the two triangles ... they being similar , find relation between distance from light of the boy  and of the shadow, given dy/dt = 4