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A spotlight on the ground shines on a wall 12 m away. If a man 2 m tall walks from the spotlight toward the building at a speed of 2.1 m/s, how fast is the length of his shadow on the building decreasing when he is 4 m from the building?
I cant figure out what db/dm is. b(building) m(man). I can solve it once I get that.

Question

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A spotlight on the ground shines on a wall 12 m away. If a man 2 m tall walks from the spotlight toward the building at a speed of 2.1 m/s, how fast is the length of his shadow on the building decreasing when he is 4 m from the building? 
I cant figure out what db/dm is. b(building) m(man). I can solve it once I get that.

anonymous · Answer

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anonymous · Answer

you know that 
$$\frac{y}{12}=\frac{2}{x}$$ and you also know 
$$x'=2.1$$so you can solve for 
$$y'$$ i think

anonymous · Answer

I need to relate distance from the building to y, not distance from the light. Its a start though.

anonymous · Answer

actually you need 
$$y'$$ the rate of the shadow against the wal.

anonymous · Answer

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