What is the Volume of a Solid of Revolution Rotated about the x-axis?

In summary, the conversation is about finding the volume of a solid obtained by rotating the area bounded by y=2-(1/2)x, y=0, x=1, x=2 about the x-axis using the disk method. The correct answer is 19pi/12.
  • #1
Joe_K
33
0

Homework Statement



Find the volume obtained by rotating the solid about the specified line.

y=2-(1/2)x, y=0, x=1, x=2, about the x-axis.

Homework Equations



I used the disk method

The Attempt at a Solution



I drew a sketch and used disk method. For the radius I used 2-(1/2)x with a height of 1, and integrated. For an answer, I came up with 5pi/4. Does this seem correct? Thanks!
 
Physics news on Phys.org
  • #2
Joe_K said:
For an answer, I came up with 5pi/4. Does this seem correct? Thanks!


I am getting a different answer. What are your bounds? What is the integrand?
 
  • #3
tylerc1991 said:
I am getting a different answer. What are your bounds? What is the integrand?

My bounds were from 1 to 2.
 
  • #4
Joe_K said:
My bounds were from 1 to 2.

That is correct. What about the integrand?
 
  • #5
Joe_K said:

Homework Statement



Find the volume obtained by rotating the solid about the specified line.

y=2-(1/2)x, y=0, x=1, x=2, about the x-axis.

Homework Equations



I used the disk method

The Attempt at a Solution



I drew a sketch and used disk method. For the radius I used 2-(1/2)x with a height of 1, and integrated. For an answer, I came up with 5pi/4. Does this seem correct? Thanks!
What do you mean by "with a height of 1" ?

What function did you integrate?
 
  • #6
SammyS said:
What do you mean by "with a height of 1" ?

What function did you integrate?

Sorry, I don't know why I typed height, I meant to say that that the bounds were 1 to 2. For the integrand I just had pi*2-(1/2)x*1 dx
 
  • #7
Joe_K said:
For the integrand I just had pi*2-(1/2)x*1 dx

The area of one of the disks is going to be [itex]\pi \cdot (2 - \frac{1}{2} x)^2[/itex]. What happens when we sum those disks from [itex]x = 1[/itex] to [itex]x = 2[/itex]?
 
  • #8
tylerc1991 said:
The area of one of the disks is going to be [itex]\pi \cdot (2 - \frac{1}{2} x)^2[/itex]. What happens when we sum those disks from [itex]x = 1[/itex] to [itex]x = 2[/itex]?

I think I forgot to square the radius when I originally did it. I redid the problem and came up with 19pi/12. Is this still wrong?
 
  • #9
Joe_K said:
I think I forgot to square the radius when I originally did it. I redid the problem and came up with 19pi/12. Is this still wrong?

That is the answer I got.
 
  • #10
Awesome. Thanks guys!
 

Related to What is the Volume of a Solid of Revolution Rotated about the x-axis?

1. What is a "Solid of Revolution Problem"?

A "Solid of Revolution Problem" is a mathematical concept that involves rotating a two-dimensional shape around an axis to create a three-dimensional solid. This problem is often encountered in calculus and is used to calculate the volume and surface area of various objects.

2. How do you solve a Solid of Revolution Problem?

To solve a Solid of Revolution Problem, you must first identify the axis of rotation and the boundaries of the shape. Then, you can use integration techniques to find the volume or surface area of the resulting solid. This process may require the use of different integration methods, such as the disk method or the shell method.

3. Can a Solid of Revolution Problem have a curved axis?

Yes, a Solid of Revolution Problem can have a curved axis. In fact, this type of problem is commonly encountered in real-world scenarios, such as finding the volume of a wine barrel or the surface area of a water tower. In these cases, the integration methods may need to be adjusted to accommodate the curved axis.

4. What are some common applications of Solid of Revolution Problems?

Solid of Revolution Problems have many practical applications in fields such as engineering, physics, and architecture. Some examples include calculating the volume of a cylindrical tank, finding the surface area of a rollercoaster track, and determining the moment of inertia of a rotating object.

5. Are there any limitations to solving Solid of Revolution Problems?

While Solid of Revolution Problems can be applied to a wide range of shapes and objects, they do have some limitations. For instance, this method may not be suitable for objects with irregular shapes or non-uniform density. In these cases, alternative methods, such as the Pappus's centroid theorem, may be used to calculate the volume or surface area.

Similar threads

  • Calculus and Beyond Homework Help
Replies
3
Views
995
  • Calculus and Beyond Homework Help
Replies
1
Views
935
Replies
6
Views
1K
  • Calculus and Beyond Homework Help
Replies
1
Views
928
  • Calculus and Beyond Homework Help
Replies
2
Views
896
  • Calculus and Beyond Homework Help
Replies
11
Views
1K
  • Calculus and Beyond Homework Help
Replies
13
Views
1K
  • Calculus and Beyond Homework Help
Replies
4
Views
965
  • Calculus and Beyond Homework Help
Replies
20
Views
2K
  • Calculus and Beyond Homework Help
Replies
9
Views
1K
Back
Top