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Homework Help: Related rates question.

  1. Oct 30, 2011 #1
    1. The problem statement, all variables and given/known data
    Sand falls from a conveyor belt at the rate of 10 m^3/min onto the top of a conical pile. The height of the pile is always three-eighths of the base diameter. How fast are the a) height and b) radius changing when the pile is 4m high?

    2. Relevant equations
    h = 3/8 * 2r

    3. The attempt at a solution
    I'm not sure where to start. I just need a small hint.
  2. jcsd
  3. Oct 30, 2011 #2


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    Homework Helper

    The question is giving you dV/dt. What's the equation for the volume of a cone in terms of r and h? That's a small hint.
  4. Oct 30, 2011 #3
    More than enough. Thanks
  5. Oct 30, 2011 #4


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    Staff Emeritus
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    Gold Member

    The rate of change of the volume of the cone is 10 m3 per minute. What is the expression for the volume of a cone in terms of its height and base radius? This will allow you determine dr/t or dh/t in terms of dV/dt.

    EDIT: two minutes too late...
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