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: Rates of change

  1. Nov 13, 2008 #1
    1. The problem statement, all variables and given/known data
    Sand is falling into a conical pile at a rate of 10 cubic feet/minute. The diameter of the cone is 3 times the altitude. At what rate is the height of the pile change when the height=15feet.

    So i was going through and I dont know if i derived it wrong, but i had



    dv/dt= pi/3 R[tex]^{2}[/tex](dh/dt) * 2pi/3 R (h)

    but when i go through and solve it all with R= 3/2h I dont get the answer form the back of the book. Is my derivative wrong? I used chain rule...
  2. jcsd
  3. Nov 13, 2008 #2


    User Avatar
    Science Advisor
    Homework Helper

    V(t)=(1/3)pi(r(t)^2)*h(t). If you do the derivative correctly, there ought to be a dr(t)/dt hanging around someplace. And why is there a '*' between the two parts of what looks like a product rule?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook