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Related rates problem help

  1. May 11, 2016 #1
    1. The problem statement, all variables and given/known data
    laddercopy.png

    A 1.9 metre ladder is leaning against a vertical wall. If the bottom of the ladder is 30 cm from the wall and is being pull away from the wall with a horizontal speed of 25 cm per second, how fast is the top of the ladder sliding down the vertical wall?

    We define the the direction up the wall to be positive, so that your answer must be negative.

    2. Relevant equations

    does this mean when x=30 cm dx/dt = 25


    3. The attempt at a solution

    this means that the wall height is 187.6 cm using pythagoras theorem

    Any help will be much appreciated
     
  2. jcsd
  3. May 11, 2016 #2

    cnh1995

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    Homework Helper

    Yes. Start with writing height of the ladder as a function of x.
     
  4. May 11, 2016 #3
    does this mean

    h=x^2+y^2

    dx/dt=2x+2y

    25=2x30+2y
    -35=2y
    y=-17.5
     
  5. May 11, 2016 #4
    I got the answer thanks :)
     
  6. May 11, 2016 #5

    cnh1995

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    Homework Helper

    Height of the ladder is h=√(L2-x2), where L=length of the ladder i.e. 1.9m.
    You can proceed by taking derivative on both sides w.r.t. time.
     
  7. May 11, 2016 #6

    Mark44

    Staff: Mentor

    The height of the wall is irrelevant to this problem.
     
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