Solving for Volume Using the Shell Method

In summary, the conversation discusses using the shell method to find the volumes of solids generated by revolving a region around a given axis. The equation x=18(y^2 - y^3) represents the region and the axis of rotation is y=8/5. The suggested solution is 2∏∫ (0 to 1) (8/5 - y) (18y^2 - 18y^3) dy, but it is mentioned that this equation does not define a bounded region and it is assumed that the region is bounded by the y-axis. However, the differential is missing in the equation, which could cause problems in the future. The conversation ends with a question about the value of the integral
  • #1
whatlifeforme
219
0

Homework Statement


use the shell method to find the volumes of the solids generated by revolving the region about the indicated axis.


Homework Equations


x=18(y^2 - y^3) about line y=8/5.


The Attempt at a Solution


2∏∫ (0 to 1) (8/5 - y) (18y^2 - 18y^3)
 
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  • #2
whatlifeforme said:

Homework Statement


use the shell method to find the volumes of the solids generated by revolving the region about the indicated axis.


Homework Equations


x=18(y^2 - y^3) about line y=8/5.i
This single equation does not define a bounded region. Was there some other line or curve given, such as the y-axis (x= 0)?


The Attempt at a Solution


2∏∫ (0 to 1) (8/5 - y) (18y^2 - 18y^3)
 
  • #3
according to the graph it appears bounded by y-axis. (x=0)
 
  • #4
Assuming that the region to be revolved is between one arch of the curve and the y-axis, your setup looks fine, except that you are missing the differential. It might not seem important now, but when you learn more techniques of integration, omitting the differential will be a big problem.

whatlifeforme said:
2∏∫ (0 to 1) (8/5 - y) (18y^2 - 18y^3) dy



What do you get for the value of your integral?
 

Related to Solving for Volume Using the Shell Method

What is the volume shell method?

The volume shell method is a mathematical technique used to calculate the volume of a solid of revolution. It involves slicing the solid into thin cylindrical shells and using the formula V = 2πrh to find the volume of each shell, then adding up the volumes of all the shells to get the total volume.

When is the volume shell method used?

The volume shell method is typically used when the solid being rotated around an axis is not a simple geometric shape, such as a cone or cylinder. It is also useful when the axis of rotation is not along the x- or y-axis.

How does the volume shell method differ from the volume disk method?

The volume disk method involves slicing a solid of revolution into thin disks and using the formula V = πr^2h to calculate the volume of each disk. The volume shell method, on the other hand, involves slicing the solid into thin cylindrical shells and using the formula V = 2πrh to calculate the volume of each shell.

What are the steps for using the volume shell method?

1. Identify the axis of rotation.2. Determine the limits of integration.3. Express the function in terms of the variable of integration.4. Set up the integral using the formula V = 2πrh.5. Integrate to find the total volume.

Can the volume shell method be used for solids with holes?

Yes, the volume shell method can be used for solids with holes as long as the holes do not intersect with the axis of rotation. In this case, the volume of the holes would need to be subtracted from the total volume calculated using the volume shell method.

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