Question

A man 6 ft tall walks at the rate of 5 ft/sec toward a streetlight that is 16 ft tall. At what rate is the length of the shadow changing when he is 10 ft from the base of the light?

Answer 1

I have a picture drawn out but I don't understand how to set up an equation and take its derivative.

Answer 2

Oh I wasnt using two variables!

Answer 3

But after I get this what do I do?

Answer 4

I think I have the right answer,
y'(t)= 6/10 *dx/dt
y'(t) = 6/10 * 5
y'(t) = 3 ft/sec

Answer 5

An excellent drawing which clearly shows the necessary relationships to solve.