How do I calculate the volume of this?

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In summary, the volume of the region bounded by y = x^2, y = 1, and the y-axis rotated around the y-axis is πy^2.
  • #1
-EquinoX-
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How do I calculate the volume of this??

What is the volume of the region bounded by y = x^2, y = 1, and the y-axis rotated around the y -axis
 
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  • #2
define a voklume function, as a function of y, by letting V(y) be that portion of the volume lying below height y. then the derivative of this function i the area of the circular face of this portion of volume, i.e. dV/dy = πr^2 where r = x = sqrt(y), so dV/dy = πy. so you guess a formula for V(y) and then plug in y = 1.
 
  • #3
I should do this using integral.. I was thinking of slicing this region vertically but then how do I represent this in integrals?? I have to take integrals from -1 to 1 right?

I would evaluate this as the integral from 0 to 1 of (1-squareroot of y)^2 dy

is that right??
 
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  • #4
Why in the world would you slice it vertically? Since it is rotated around the y-axis, slices horizontally will be disks with radius x. Each would have area [itex]\pi x^2= \pi y[/itex] and each infinitesmal disc will have volume [itex]\pi y dy[/itex]. Integrate that.
 
  • #5
HallsofIvy said:
Why in the world would you slice it vertically? Since it is rotated around the y-axis, slices horizontally will be disks with radius x. Each would have area [itex]\pi x^2= \pi y[/itex] and each infinitesmal disc will have volume [itex]\pi y dy[/itex]. Integrate that.


I am sorry that's my mistake. I would slice it horizontally and take the integral from 0 to 1. And shouldn't the radius be 1-square root of y?? Because it's the intersection of y = x^2 and y = x
 
  • #6
-EquinoX- said:
I am sorry that's my mistake. I would slice it horizontally and take the integral from 0 to 1. And shouldn't the radius be 1-square root of y?? Because it's the intersection of y = x^2 and y = x
Where did you get y= x from? Your original post was:

-EquinoX- said:
What is the volume of the region bounded by y = x^2, y = 1, and the y-axis rotated around the y -axis
Every horizontal "slice" is a circle with center at the y-axis, x= 0, and the end of a radius at [itex]x= \sqrt{y}[/itex]. Of course, the area of the disk is [itex]\pi x^2= \pi y[/itex].
 

FAQ: How do I calculate the volume of this?

1. How do I calculate the volume of a cube?

To calculate the volume of a cube, you need to know the length, width, and height of the cube. The formula for volume is V = l x w x h, where l is the length, w is the width, and h is the height. Simply multiply these three values together to find the volume of the cube.

2. How do I calculate the volume of a cylinder?

To calculate the volume of a cylinder, you need to know the radius and height of the cylinder. The formula for volume is V = π x r^2 x h, where π is approximately 3.14, r is the radius, and h is the height. First, square the radius, then multiply it by π, and finally multiply that value by the height to find the volume of the cylinder.

3. How do I calculate the volume of a sphere?

To calculate the volume of a sphere, you need to know the radius of the sphere. The formula for volume is V = 4/3 x π x r^3, where π is approximately 3.14 and r is the radius. First, cube the radius, then multiply it by π, and finally multiply that value by 4/3 to find the volume of the sphere.

4. How do I calculate the volume of a rectangular prism?

To calculate the volume of a rectangular prism, you need to know the length, width, and height of the prism. The formula for volume is V = l x w x h, where l is the length, w is the width, and h is the height. Simply multiply these three values together to find the volume of the rectangular prism.

5. How do I calculate the volume of an irregular-shaped object?

To calculate the volume of an irregular-shaped object, you can use the water displacement method. Fill a graduated cylinder with water and record the initial volume. Then, place the object in the cylinder and record the new volume. The difference between the two volumes is the volume of the object. Alternatively, you can use a formula or computer software to calculate the volume of an irregular-shaped object.

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