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: Volume rate problem

  1. Mar 31, 2008 #1
    1. The problem statement, all variables and given/known data

    The radius r of a sphere is increasing at a rate of 2 inches per minute. Find the rate of chance of the volume when r=6 and r=24 inches.

    2. Relevant equations


    3. The attempt at a solution

    This is what I did, I would appreciate it if someone could tell me if it is correct.

    So the volume of a sphere is V=(4/3)(pi)(r^3)

    So the first thing I did was derive the equation and got this...


    Simplifying it and plugging in 2 for (dr/dt) i got...


    So then I just plugged in the r and got 288pi and 4680pi, I have a feeling I've done this terribly wrong though :(
  2. jcsd
  3. Mar 31, 2008 #2
    I didn't check your numbers, but your method seems fine to me. However, you might want to get a second opinion before you go and write it in stone.
  4. Mar 31, 2008 #3
    It all looks good to me to. Except for when the radius is 24 I got 4608. Maybe you just had a typo there?
  5. Mar 31, 2008 #4
    yes sorry that was a typo, thanks! :)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook