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!

Percent increase/decrease cylinder (no values)

  1. Feb 6, 2010 #1
    By approximately what percent would the volume of a right circular cylinder increase or decrease if the height were to increase by 2% and the radius of the base were to decrease by 1.5%?

    Partial differentials makes sense in this case, I am just stuck when I have no usable values.

    Volume of a cylinder = [tex]\pi[/tex]r2h
    dV = [tex]\pi[/tex]r2dh + 2[tex]\pi[/tex]r dr

    dh = 1.02
    dr = .985

    I'm stuck in how to translate this in a comparable way to the original cylinder. Any suggestions are welcome!
  2. jcsd
  3. Feb 6, 2010 #2


    User Avatar
    Homework Helper

    Recheck your expression for dV.

    When you do that divide the left side by V and the right side by πr2h and then you can find the percentage.
  4. Feb 6, 2010 #3


    User Avatar
    Science Advisor
    Homework Helper

    No, no. dh isn't 1.02, dh/h is 0.02. And the quantity you want to find is the percentage change. That's dV/V.
  5. Feb 6, 2010 #4
    Okay, the only reason I did 1.02 is because I thought of doing I could express is as a negative/positive percentage. This was obviously a bad move and doesn't make any sense. But I got it now. Thanks for the help everyone!
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook