This function fails the conservative test, yet it is path independent?

In summary, the conversation discusses a homework problem involving a line integral and the evaluation of \int_C tan(y) dx + x sec^2 (y) dy. It is determined that the force involved is conservative, based on the given information.
  • #1
flyingpig
2,579
1

Homework Statement



Show that the line integral is path independent and evaluate the integral

[tex]\int_C tan(y) dx + x sec^2 (y) dy[/tex]

The Attempt at a Solution



[tex]\frac{\partial }{\partial x}(tan(y)) = 0 \neq 2xsec^2(y)tan(y) = x\frac{\partial }{\partial y}(sec^2(y))[/tex]
 
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  • #2
I believe your problem is stemming from the presence of the differentials, dx and dy. The general form of a line integral is the following:
[tex]
\int_C M dx + N dy
[/tex]

Where M & N relate to the quantities in your problem such that:

M = [tex]tan(y)[/tex]
N = [tex]x sec^2 (y)[/tex]

Now we know for a force to be conservative it must satisfy the following relationship:

[tex]\frac{\partial M }{\partial y} = \frac{\partial N }{\partial x}[/tex]

Given this information, is your force conservative?

Hope this helps.

Joe
 

1. Why is this function failing the conservative test?

The conservative test is used to determine if a function is path independent, meaning that the integral of the function along a closed path is equal to zero. If a function fails this test, it means that the integral is not equal to zero, indicating that the path does matter in the calculation.

2. Can you provide an example of a function that fails the conservative test but is still path independent?

Yes, a common example is the function f(x,y) = -y^2/2 + x^2. This function fails the conservative test because when integrated along a closed path, the integral is equal to 2π instead of zero. However, this function is still path independent because the value of the integral only depends on the endpoints, not on the path itself.

3. How does a function being path independent affect its usefulness in real-world applications?

In real-world applications, path independence is a desirable property for a function to have. This means that the path taken to get from one point to another does not affect the final outcome, making calculations and predictions easier and more reliable. Functions that fail the conservative test may still be useful, but they may require more complex calculations and may not be as accurate.

4. What are some potential reasons for a function to fail the conservative test?

A function may fail the conservative test for a variety of reasons. One common reason is that the function is not continuous or differentiable at some point, which can lead to unexpected results when integrating along a path. Another reason could be that the function is defined on a domain where the conservative test does not apply, such as a function with a singularity or a function with a discontinuity.

5. Are there any other tests or methods for determining if a function is path independent?

Yes, there are other tests and methods that can be used to determine if a function is path independent. One is the gradient test, which involves taking the gradient of the function and checking if it is equal to zero. Another method is using line integrals to check if the function is independent of the path taken. Additionally, there are specific conditions and properties that a function must satisfy in order to be path independent, such as being a conservative vector field or satisfying the Cauchy-Riemann equations.

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