Constant Rate of Change in Area of Circle with Changing Radius?

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Homework Help Overview

The problem involves a circular ripple created by a stone dropped into a pond, with the radius increasing at a constant rate of 3 ft/s. The central question is whether the area of the circle also increases at a constant rate.

Discussion Character

  • Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the relationship between the radius and area of a circle, with attempts to differentiate the area with respect to time. Questions arise about the constancy of the rate of area change in relation to the radius.

Discussion Status

Some participants have provided insights into the mathematical relationships involved, noting that the rate of change of area is dependent on the radius. There is an acknowledgment of confusion regarding the constancy of the area change rate, with some clarification offered.

Contextual Notes

Participants express uncertainty about the implications of the variable nature of the area change rate as it relates to the radius. The discussion reflects an exploration of assumptions about constant rates in the context of changing dimensions.

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Homework Statement


A stone dropped into a still pond sends out a circular ripple whose radius increases at a constant rate of 3 ft/s. Does the area also increase at a constant rate?


Homework Equations


A = ∏r2

The Attempt at a Solution


dA/dt = 2∏r(dr/dt)
dA/dt = 2∏r(3ft/s)

What now?
 
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Wa1337 said:

Homework Statement


A stone dropped into a still pond sends out a circular ripple whose radius increases at a constant rate of 3 ft/s. Does the area also increase at a constant rate?


Homework Equations


A = ∏r2

The Attempt at a Solution


dA/dt = 2∏r(dr/dt)
dA/dt = 2∏r(3ft/s)

What now?

Now you answer the question - Is the area increasing at a constant rate?
 
I mean, I guess it would, but I don't really know how to explain it.
 
The radius is increasing at a constant rate, since dr/dt = 3 (ft/sec).

The rate of change of the area is dA/dt = 6\pir (ft2/sec). Does that look like a constant to you?
 
Yes.
 
A constant value shouldn't have a variable in it. The value of dA/dt depends on how big the circle is - IOW, dA/dt is NOT constant.
 
Ok thanks I was very confused on this but you helped.
 

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