A 6 ft tall person walks away from a 10 ft lamppost at a constant rate of 5 ft/s. What is the rate (in ft/s) that the tip of the shadow moves away from the pole when the person is 10 ft away from the pole?

Question

I have drawn out the picture, but I am not sure where in fact ot get the equation?s

Answer 1

Does your picture show the similar triangles (the big triangle made by the light post light to the end of the person's shadow... and the little triangle the person makes with his own shadow)? If so then dx/dt = 5 ft/s, and we need ds/dt when x = 10.