Posted by **sara** on Tuesday, October 16, 2012 at 2:53am.

A street light is mounted at the top of a 6-meter-tall pole. A man 2 m tall walks away from the pole with a speed of 1.4 m/s along a straight path. How fast is the tip of his shadow moving when he is 16 m from the pole?

- calculus -
**Reiny**, Tuesday, October 16, 2012 at 9:18am
same question ....

http://www.jiskha.com/display.cgi?id=1333489636

just change the necessary numbers

- calculus -
**Steve**, Tuesday, October 16, 2012 at 11:04am
since you have a calculus class, you probably ought to do it Reiny's way, but sometimes a little simplification can save you some work:

If the man is x away from pole, ad his shadow length is s, then using similar triangles,

s/2 = (x+s)/6

s = 1/2 x

so, ds/dt = 1/2 dx/dt

since the tip of the shadow is x+s from the pole, it is moving at

dx/dt + ds/dt = dx/dt + 1/2 dx/dt = 3/2 dx/dt = 3/2(1.4) = 2.1 m/s

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