Calculating Rate of Change for Sphere Volume and Surface Area

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Homework Help Overview

The discussion revolves around calculating the rate of change of a sphere's volume and surface area, specifically focusing on the relationships defined by the formulas for volume \( V = \frac{4}{3}\pi r^3 \) and surface area \( A = 4\pi r^2 \). Participants are exploring how to derive the rate of change of volume with respect to surface area.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants are attempting to apply the chain rule to find \( \frac{dV}{dA} \) by first calculating \( \frac{dV}{dr} \) and \( \frac{dA}{dr} \). There are questions about the correctness of derivatives and the process of dividing these rates to find the desired rate of change.

Discussion Status

There is an ongoing exploration of the derivatives involved, with some participants providing calculations for \( \frac{dV}{dr} \) and \( \frac{dA}{dr} \). While some guidance has been offered regarding the use of the chain rule, there is no explicit consensus on the final approach or solution.

Contextual Notes

Some participants express frustration over the nature of assistance being provided, indicating a desire for a more collaborative exploration rather than direct solutions. The discussion also includes a separate mention of a different topic related to catalytic oxidation, which may indicate a shift in focus or confusion in the thread.

freman1075
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hi everyone,
i am having trouble with this rate of change question.
I need to find the rate of change of a sphere with a volume of V= 4/3*pi*r^3 in respect to it's surface area of A= 4*pi*r^2
can anyone give me a hand?
Thanks
 
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Since the surface area- the derivative of the volume-is A=4*pi*r^2, it would seem that change there would be the derivative, 8*pi*r.
 
freman1075 said:
hi everyone,
i am having trouble with this rate of change question.
I need to find the rate of change of a sphere with a volume of V= 4/3*pi*r^3 in respect to it's surface area of A= 4*pi*r^2
can anyone give me a hand?
Thanks

So you want to find dV/dA? Use the chain rule dV/dr= (dV/dA)(dA/dr) so dV/dA= (dV/dr)/(dA/dr). Find dV/dr and dA/dr and divide.
 
HallsofIvy said:
So you want to find dV/dA? Use the chain rule dV/dr= (dV/dA)(dA/dr) so dV/dA= (dV/dr)/(dA/dr). Find dV/dr and dA/dr and divide.

so if dV/dr = 4*pi*r^2
and if dA/dr = 8*pi*r

i just divide the two?
 
freman1075 said:
hi everyone,
i am having trouble with this rate of change question.
I need to find the rate of change of a sphere with a volume of V= 4/3*pi*r^3 in respect to it's surface area of A= 4*pi*r^2
can anyone give me a hand?
Thanks

dv/dr = 4/3*pi*3*r^2 = 4*pi*r^2

da/dr = 4*pi*2*r = 8*pi*r

dv/da = dv/dr * dr/da = r/2
 
HallsofIvy said:
So you want to find dV/dA? Use the chain rule dV/dr= (dV/dA)(dA/dr) so dV/dA= (dV/dr)/(dA/dr). Find dV/dr and dA/dr and divide.

freman1075 said:
so if dV/dr = 4*pi*r^2
and if dA/dr = 8*pi*r

i just divide the two?
Well, that is what I said in the post you quoted!

Lizzie, when a person asks for help, please do not just do the problem for them!
 
ok sorry hallsofivy
 
to find the rate of change for designing of catalytic oxidation converter
SO2+0.5O2 <---->SO3
 

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