(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A girl 5 feet tall is running at the rate of 12 feet/second and

passes under a street light 20 feet above the ground. Find how

rapidly the length of her shadow is increasing when she is 20

feet past the base of the street light.

3. The attempt at a solution

I let the distance of girl from light be S = 12t

I let the distance of shadow from light be X,

Due to similar triangle,

[itex]\frac{x}{x-12t} = \frac{20}{5}[/itex]

[itex]-15x=-240t[/itex]

[itex]x=16t[/itex]

[itex]\frac{dx}{dt}=16[/itex]

But the ans is 4ft/sec any clues as to where I went wrong?

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# Homework Help: Speed of moving shadow due to light source

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