Find out the volume of the solid- method of rings, Mathematics

Assignment Help:

Find out the volume of the solid obtained by rotating the region bounded by y = x2 - 2x and  y = x about the line y = 4 .

Solution: Firstly let's get the bounding region & the solid graphed.

605_solid graphed.png

Again, we will be looking for the volume of the walls of this object. Also since we are rotating around a horizontal axis we know that the cross-sectional area will be a function of x.

Given are a couple of sketches of the boundaries of the walls of this object in addition to a typical ring. The sketch on the left involved the back portion of the object to specify a little context to the figure on the right.

1364_solid graphed 1.png

Now, we have to be careful here in finding out the inner & outer radius. Let's begin with the inner radius as this one is little clearer.  Firstly, the inner radius is not x. The distance from x-axis to the inner edge of the ring is x, however we desire the radius and i.e. the distance from the axis of rotation to the inner edge of the ring.  Therefore, we know that the distance from the axis of rotation to the x-axis is 4 & the distance from the x-axis to the inner ring is x. The inner radius have to be then be the difference among these two.  Or,

                                   inner radius = 4 - x

The outer radius works the similar way.  The outer radius is,

outer radius = 4 - ( x2 - 2 x ) = - x2 + 2 x + 4

 Note as well that given the location of the typical ring in the sketch above the formula for the outer radius might not look quite right however it is actually correct.  As sketched the outer edge of the ring is below the x-axis & at this point the value of the function will be negative and therefore when we do the subtraction in the formula for the outer radius we'll in fact be subtracting off a negative number that has the net effect of adding this distance onto 4 and which gives the correct outer radius. Similarly, if the outer edge is above x-axis, the function value will be positive and therefore we'll be doing an honest subtraction here and again we'll get the accurate radius in this case.

The cross-sectional area for this case is following,

A ( x ) = ∏ ((- x2 + 2x + 4)2  - ( 4 - x )2 ) = ∏ ( x4 - 4 x3 - 5x2 + 24 x )

The first ring will take place at x =0 and the last ring will take place at x = 3 and therefore these are our limits of integration. The volume is then,

V = ∫ab A(x)dx

  = ∏∫ 3x4 - 4x3  - 5x2 + 24x dx

   = ∏  (1/5 x5 - x4 - 5/3 x3 + 12x2 )|30

     = 153 ∏ /5


Related Discussions:- Find out the volume of the solid- method of rings

Personal assistance needed, I have an original finding on the subject of pr...

I have an original finding on the subject of prime distribution and would like expert help in my endeavors. I have written a paper describing everything in detail and demonstration

Determine the properties and query are definable in datalog, We now focus o...

We now focus on the use of Datalog for defining properties and queries m graphs. (a) Suppose that P is some property of graphs definable in Datalog. Show drat P is preserved und

What is the maximum number calories which consume from fats, Josephine is o...

Josephine is on an 1,800 calorie per day diet. She tries to remain her intake of fat to no more than 30% of her overall calories. Based on an 1,800 calorie a day diet, what is the

Classify linear or nonlinear, Question: Classify the following differen...

Question: Classify the following differential equations as linear/nonlinear. Also, what is the order of the following differential equations? Xy'-2y =x Xy'' -2y' =xsin(y)

Student, Patio measures 24 meters square. Patio stone are 30 cm each side. ...

Patio measures 24 meters square. Patio stone are 30 cm each side. How many stones are required to cover the patio?

Geometry, calculate the area of a trapezoid with height 8cm base 18cm and 9...

calculate the area of a trapezoid with height 8cm base 18cm and 9cm

Algorithm, what does algorithm refer to

what does algorithm refer to

Volume of grains in the silo , The volume of grains in a silo at a particul...

The volume of grains in a silo at a particular time (measured in hours) is given by V (t) = 4t(3-t) m3. Find the rate of change of the volume of grains in the silo from first princ

Doubles Plus 1 and Doubles Minus 1, Write the doubles fact you used to solv...

Write the doubles fact you used to solve the problem. 7 + 8 = 15

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd