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Homework Help: Word problem-I would like to check my procedure

  1. Oct 15, 2009 #1
    word problem-Please help me to check my procedure

    1. The problem statement, all variables and given/known data

    A cubical ice block is melting at a rate that relates to its surface area. Set up an equation for the volume of a cube, C, in terms of its surface area, S.

    2. Relevant equations


    3. The attempt at a solution

    let length of the side of the cube:x
    dC/dx=3x^2 dS/dx=12x dC/dS=x/4
    Now what should I do? I think I did pretty well untill now. How should I use this information for getting the answer? Or dC/dS(which is x/4) is the final answer?
    Last edited: Oct 15, 2009
  2. jcsd
  3. Oct 15, 2009 #2


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    Homework Helper
    Education Advisor
    Gold Member

    You are almost half-way there, and this is not a calculus problem.

    Work with S and find a formula for x.
  4. Oct 15, 2009 #3
    Thank you. But work with S? Would you mind if I want more specific explanation from you? Sorry, cause I am not very good at math, interpreting word problems.
  5. Oct 15, 2009 #4


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    The problem said "Set up an equation for the volume of a cube, C, in terms of its surface area, S". That's why you need to "work with S".
    You have [itex]C= x^3[/itex]. You also know that [/itex]S= 6x^2[/itex].

    Solve [itex]S= 6x^2[/itex] for x (which is a length and so positive) and replace the "x" in [itex]C= x^3[/itex] with that/
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