- #1
hqjb
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Homework Statement
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.
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?