Volume of a Solid By Revolution

In summary, the problem asks to find the volume of a solid generated by revolving the region bounded by the curves y=-x^2+4x-3 and y=0 around the line x=-1. The shell method is used, with the integration variable determining the radius and the function value determining the height of the shell. The resulting integral is 2pi * ∫(x+1)(-x^2+4x-3)dx.
  • #1
Justabeginner
309
1

Homework Statement


Find the volume of the solid generated by revolving about the line x=-1, the region bounded by the curves y=-x^2 + 4x - 3, and y=0.


Homework Equations


Shell Method?


The Attempt at a Solution



V= 2pi * ∫x* f(x) dx, where a and b are the lower and upper limits of integration, respectively.
I'm not even sure if what I'm doing is right. And how do I know to use dx or dy? Guidance please?
 
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  • #2
Shell Method?
Okay
V= 2pi * ∫x* f(x) dx, where a and b are the lower and upper limits of integration, respectively.
What does the single x there represent in your shells?
Hint: if you rotate around x=-1 instead of x=0, you have to change this.
And how do I know to use dx or dy?
Do you have constant x or constant y within your shells? That is fine.
 
  • #3
The x represents the radius, and so I would have to add 1 (- -1)? But I don't even understand what quantity defines the radius here. Is it the -x^2+4x-3? There is no constant given, but I presumed I should use dx since the problem is rotating around the x=-1 line (shift of x-axis left 1 unit).
 
  • #4
and so I would have to add 1
Right.
But I don't even understand what quantity defines the radius here.
The integration variable ("dx") determines that radius.
The function value (-x^2+4x-3) is the "height" of the shell.
 
  • #5
So I would end up with

2 pi * integral sign [(x+1) (-x^2 + 4x-3) dx] ? Is that really it? o.0 I thought it's more intricate.
 
  • #6
Most problems are easy, if you know how to solve them.
 
  • #7
Wow, thank you so much mfb. I appreciate it.
 

Related to Volume of a Solid By Revolution

What is the volume of a solid by revolution?

The volume of a solid by revolution is the amount of space occupied by the solid when it is rotated around a specific axis. It is a measure of the three-dimensional space inside the solid.

What is the formula for calculating the volume of a solid by revolution?

The formula for calculating the volume of a solid by revolution is V = π∫ab (f(x))2dx, where a and b are the limits of integration, f(x) is the function representing the cross-sectional area of the solid, and π is the constant pi.

What is the axis of revolution?

The axis of revolution is the imaginary line around which the solid is rotated. It can be any line passing through the solid's center of mass or any other point on its surface.

Can the volume of a solid by revolution be negative?

No, the volume of a solid by revolution cannot be negative. It is always a positive value as it represents the amount of space occupied by the solid.

What are some real-life applications of calculating the volume of a solid by revolution?

Calculating the volume of a solid by revolution is used in various fields such as engineering, architecture, and physics. It is used to design and analyze structures like bridges, buildings, and tunnels. It is also used in the study of rotational motion and fluid dynamics.

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