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

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In summary, a stone dropped into a still pond creates a circular ripple with a radius that increases at a constant rate of 3 ft/s. The question is whether the area also increases at a constant rate. Using the equation A = ∏r^2 and the rate of change formula dA/dt = 2∏r(dr/dt), we can see that the rate of change of the area is not constant, as it depends on the size of the circle. Therefore, the area is not increasing at a constant rate.
  • #1
Wa1337
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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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  • #2
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?
 
  • #3
I mean, I guess it would, but I don't really know how to explain it.
 
  • #4
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[itex]\pi[/itex]r (ft2/sec). Does that look like a constant to you?
 
  • #5
Yes.
 
  • #6
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.
 
  • #7
Ok thanks I was very confused on this but you helped.
 

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

1. What is the formula for calculating the area of a circle?

The area of a circle is calculated by multiplying pi (π) by the square of the radius (r), or A = πr^2.

2. How does the area of a circle change when the radius changes?

The area of a circle is directly proportional to the square of the radius. This means that as the radius increases, the area also increases, and as the radius decreases, the area decreases.

3. What is meant by "related rates" in the context of finding the rate of change of the area of a circle?

Related rates refer to the relationship between two changing quantities. In the context of finding the rate of change of the area of a circle, the radius and the area are related to each other and are both changing over time.

4. How do you find the rate of change of the area of a circle with respect to time?

To find the rate of change of the area of a circle with respect to time, you can use the related rates formula: dA/dt = 2πr(dr/dt). This formula takes into account the changing radius and the constant value of pi (π).

5. Can the rate of change of the area of a circle ever be negative?

No, the rate of change of the area of a circle can never be negative. The area of a circle is always a positive value, and as the radius increases or decreases, the area will also increase or decrease, respectively.

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