Calculus Definite Integrals: Volumes by Washer Method

In summary, when using the Washer Method to revolve a region R bounded by y=x^2 and y=x^.5 about the line y=-3, the outer radius of the washers is given by ##\sqrt x + 3## and the inner radius is ##x^2 + 3##. The volume can be calculated using the formula V = pi * integral of (outer radius)^2 - (inner radius)^2 dx from 0 to 1.
  • #1
jsun2015
10
0

Homework Statement


Using Washer Method: Revolve region R bounded by y=x^2 and y=x^.5 about y=-3



Homework Equations


V= integral of A(x) from a to b with respect to a variable "x"
A(x)=pi*radius^2


The Attempt at a Solution


pi(integral of (x^.5-3)^2 -(x^2)^2-3) from 0 to 1 with respect to x

The answer involves x^.5+3 instead of x^.5 -3. I don't understand why you would add instead of subtract 3; y decreased from 0 to -3 when revolved around y=-3
 
Physics news on Phys.org
  • #2
Make a drawing. See that the outer radius of your washers is ##\sqrt x + 3## and the inner is ## x^2 + 3##
 
  • #3
jsun2015 said:
The answer involves x^.5+3 instead of x^.5 -3. I don't understand why you would add instead of subtract 3; y decreased from 0 to -3 when revolved around y=-3

The length of a vertical line is ##y_{upper}-y_{lower}##. Also don't forget to square your second term.
 

FAQ: Calculus Definite Integrals: Volumes by Washer Method

1. What is the washer method in calculus?

The washer method is a technique used in calculus to find the volume of a solid of revolution by slicing the solid into thin discs or washers and integrating the cross-sectional area of each disc.

2. When is the washer method used?

The washer method is typically used when finding the volume of a solid that is formed by rotating a bounded area around a specific axis. It is commonly used in problems involving cylinders, cones, and spheres.

3. How do you set up the integral for the washer method?

To set up the integral for the washer method, you first need to determine the limits of integration, which are typically the bounds of the area being rotated. Then, you need to find the radius and height of each washer and set up the integral using the formula V = ∫abπ(Router)2-π(Rinner)2 dx or dy, depending on the axis of rotation.

4. What is the difference between the washer method and the disk method?

The main difference between the washer method and the disk method is that the washer method can be used for solids of revolution with a hole or empty space in the middle, while the disk method can only be used for solids of revolution with no empty space.

5. Can the washer method be used for non-circular shapes?

Yes, the washer method can be used for non-circular shapes as long as the cross-sectional area can be represented by a function that can be integrated. For example, it can be used for finding the volume of a wine bottle, which has a curved shape that is not circular.

Similar threads

Back
Top