1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: (repost since typos) Volume of revolution using shell method

  1. Nov 1, 2009 #1
    1. Use the shell method to find the volume of the solid generated by revolving about the y-axis. [tex]x=y^2, x=y+2[/tex]

    2. same as #1, except change y and x for the two equations and revolve about x-axis.

    I tried doing [tex]2pi\int_{x=0}^4(x)(\sqrt{x}-x+2)dx[/tex] but the answer is off for #1.

    I tried doing [tex]2pi\int_{y=-1}^4(y)(\sqrt{y}-y+2)dy[/tex], well it's wrong.

    Is there a problem with how I established the shell height?

    the answer for these two questions are supposed to give me 72pi/5.
  2. jcsd
  3. Nov 1, 2009 #2


    User Avatar
    Science Advisor
    Homework Helper

    Hi Call my name! :smile:

    (have a pi: π and a square-root: √ and try using the X2 tag just above the Reply box :wink:)
    Yeees … it's the shell width, isn't it? :wink:
    Are you sure that's the question? If you swap everything, isn't the volume the same?:smile:
  4. Nov 1, 2009 #3
    Yeah, I meant that those two questions' answers are the same.

    So is what I have established wrong?
  5. Nov 1, 2009 #4


    User Avatar
    Science Advisor
    Homework Helper

    You've used height instead of width

    (or you've revolved around the wrong axis).
  6. Nov 1, 2009 #5
    What do you mean? I'm a newbie so please specify and clarify
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook