Results 1 to 3 of 3

Math Help - help with word problem?

  1. #1
    Senior Member
    Joined
    Apr 2009
    Posts
    253

    help with word problem?

    The number of liters of water remaining in a tank t minutes after the tank has started to drain is R(t)=2t^3-20t^2-72t+820. At what moment is the water draining the fastest?

    the first thing i think of is to take the derivative but then after that i dont know what to do.

    i took 2nd derivative then set it to 0
    then i get
    x= 10/3
    Last edited by yoman360; January 16th 2010 at 01:21 PM.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Dec 2009
    Posts
    3,120
    Thanks
    1
    The derivative gives you the rate of change of the water volume.
    You want to find the maximum value of this change.
    Hence you must calculate the 2nd derivative and set it to zero.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Master Of Puppets
    pickslides's Avatar
    Joined
    Sep 2008
    From
    Melbourne
    Posts
    5,236
    Thanks
    28
    Quote Originally Posted by yoman360 View Post

    the first thing i think of is to take the derivative but then after that i dont know what to do.
    You need to find where the gradient function is a max, therefore take the derivative again, set it to zero and solve for t.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. word problem - the snow plough problem?
    Posted in the Differential Equations Forum
    Replies: 1
    Last Post: October 13th 2011, 02:02 PM
  2. Replies: 3
    Last Post: January 2nd 2011, 09:20 PM
  3. 1 Word problem and 1 function problem
    Posted in the Algebra Forum
    Replies: 8
    Last Post: April 21st 2010, 09:01 AM
  4. Replies: 2
    Last Post: January 10th 2009, 06:49 AM

Search Tags


/mathhelpforum @mathhelpforum