Integrals and The Washer Method

In summary, the problem is asking to find the volume of a solid using the Washer Method, with the given functions and boundaries. The red line segment represents the difference between the larger and smaller x values, and the problem is revolving around the y-axis. The volume of each washer can be calculated using the formula pi(R(x)^2 - r(x)^2)*delta_y, with R(x) = sqrt(3) and r(x) = sqrt(3 - y^2). The washers extend from y = 0 to y = sqrt(3).
  • #1
erok81
464
0

Homework Statement



Find the volume of the solid using The Washer Method

[tex]y=x^2, x=2[/tex]

Homework Equations





The Attempt at a Solution



I can solve this problem fine and I don't think my actual question even affects the solution, but I would like to know how one does this.

In my textbook they say to setup the problem on a graph, no problem there. But I am confused on how one obtains the inner line segment.

Actually here is a drawing since I can't explain what I am looking for.

Untitled.png


How do you find that red line segment? I would think that would matter in the solution, but it doesn't seem to - at least at my level.
 
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  • #2
The length of the red line segment is 2 - sqrt(y), which is the difference of the larger x value (2) and the smaller x value (sqrt(y)).

You haven't described the region whose volume you want to find. Is the area you show to be revolved around the x-axis or the y-axis, or even some other line?

From the red line segment you show, it would seem that your region is being revolved around the y-axis.
 
  • #3
Actually let me ask a real problem question. My prof failed to teach any of this to us, so I am having to learn this on my own.

Here is the problem.

The region in the first quadrant is bounded on the left by the circle [tex]x^2 + y^2 =3[/tex], on the right by the line x=sqrt(3), and above by the line y=sqrt(3).

I can draw the picture fine, but I don't understand to figure out R(x) and r(x) to solve. Any hints so I can get it setup?

Object is revolving about the y-axis.
 
  • #4
Mark44 said:
The length of the red line segment is 2 - sqrt(y), which is the difference of the larger x value (2) and the smaller x value (sqrt(y)).

You haven't described the region whose volume you want to find. Is the area you show to be revolved around the x-axis or the y-axis, or even some other line?

From the red line segment you show, it would seem that your region is being revolved around the y-axis.

Got it. And yes it is revolving around the y-axis. I didn't know anything about the red line except it was placed there in my answer book. :)
 
  • #5
Each washer has a volume of pi(R(x)^2 - r(x)^2)*delta_y,
[tex]\Delta V = \pi[(R(x)^2 - r(x)^2]\Delta y[/tex]
where R(x) = sqrt(3) and r(x) = sqrt(3 - y^2).



Your washers extend from y = 0 to y = sqrt(3).
 

FAQ: Integrals and The Washer Method

What is the Washer Method and how is it used in integration?

The Washer Method is a technique used in integration to find the volume of a solid of revolution. It involves slicing the solid into infinitesimally thin discs or washers, finding the volume of each disc, and then adding them all together to get the total volume.

What is the difference between the Washer Method and the Shell Method?

The main difference between the Washer Method and the Shell Method is the shape of the infinitesimal slices used to calculate the volume. The Washer Method uses discs or washers, while the Shell Method uses cylindrical shells. Both methods can be used to find the volume of a solid of revolution, but they may be more efficient for different types of functions.

When should I use the Washer Method in integration?

The Washer Method is typically used when the cross-section of the solid is perpendicular to the axis of revolution. It is also useful when the function being integrated is defined in terms of the perpendicular axis, making the calculation of the volume of each disc or washer simpler.

What are some common mistakes to avoid when using the Washer Method?

One common mistake when using the Washer Method is forgetting to account for the inner and outer radii of the washers. It is important to correctly identify which radius corresponds to the inner and outer edge of the solid, as this will affect the calculation of the volume. Additionally, forgetting to take into account any intersections or holes in the solid can also lead to incorrect results.

Can the Washer Method be used for solids with irregular shapes?

Yes, the Washer Method can be used for solids with irregular shapes by breaking the solid into smaller, simpler shapes and using the method to find the volume of each shape. These volumes can then be summed together to find the total volume of the irregular solid.

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