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Related rates question, shadow

  1. Mar 8, 2010 #1
    1. The problem statement, all variables and given/known data
    A man 6m tall walks away from a light 10m above the ground. If his shadow lengthens at a rate of 2m/s, how fast is he walking?


    2. Relevant equations



    3. The attempt at a solution
    I have nothing.
     
  2. jcsd
  3. Mar 8, 2010 #2

    cronxeh

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    Gold Member

    Using similar triangles you can find the relationship between the shadow length (B) and distance away from pole (A).


    Keeping in mind that you are given dB/dt and asked to find dA/dt
     
    Last edited: Aug 21, 2010
  4. Mar 8, 2010 #3
    but how can i use similar triangles if i only have one of the dimensions of the triangle?
     
  5. Mar 8, 2010 #4

    cronxeh

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    Gold Member

    Look at the picture I attached. The relationship between ratios is constant, therefore the relationship between speed of man and length of shadow is constant
     
  6. Mar 8, 2010 #5
    ahhhh and the light goes on. thankyou!
     
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