# Homework Help: Volume Of solids question help

1. Sep 2, 2011

### joe007

Volume Of solids question help!!

1. The problem statement, all variables and given/known data

i) find the area enclosed by the curves y=x^1/2 and y=x^4
ii)find the volume of the solid when the area in part (i) is rotated about the the line x=2

2. Relevant equations
V=PI*y^2dx

3. The attempt at a solution
wel the area is simple integral 0 to1 root x -x^.5 and i got 7/15

but im not sure how to calculate the volume about x=2

2. Sep 2, 2011

### tiny-tim

hi joe007!
slice the volume into horizontal "washers" of height dy, and integrate

3. Sep 2, 2011

### HallsofIvy

Re: Volume Of solids question help!!

Equivalent to "washers": Use "disks" to find the volume when $y= x^{1/2}$ is rotated around the x-axis, then use "disks" to find the volume when $y= x^4$ is rotated around the x-axis, and subtract.

4. Sep 2, 2011

### joe007

Re: Volume Of solids question help!!

so its V=2PI* (integral 0 to 2) (x-2)x^0.5 -(x-2)x^4 dx

5. Sep 2, 2011

### joe007

Re: Volume Of solids question help!!

i think it should be from 0 to 1

6. Sep 2, 2011

### SammyS

Staff Emeritus
Re: Volume Of solids question help!!

Correct !