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: Growth Problem

  1. Feb 2, 2006 #1
    I am having a problem with finding the constant K in This problem.

    The time rate of change of an alligator population P in a swamp is proportional to the square root of P. The swamp contains 9 alligators in 2000 and 25 alligators in 2005. When will there be 44 alligators in the swamp?

    I have determined the formula dP/dT = KP^1/2

    P(0)=9, P(5)=25

    P^-1/2dP = Kdt and 2P^1/2=C + Kt

    A simple push with how to introduce the values into this equation would be greatly appreciated.
  2. jcsd
  3. Feb 2, 2006 #2
    If I'm not mistaken...
    [tex]2\sqrt{p} = c + kt [/tex]
    if t = 0, then p = 9, and the kt term disappears, so you can get a value for C. Then do the same kind of thing for the value of k using the other piece of data you are given.
  4. Feb 2, 2006 #3


    User Avatar
    Science Advisor

    Two unknowns, C and K, so you need two equations. You are given two pieces of information. As finchie_88 suggested (although he didn't say it explicitely), let t be the number of years since 2000. Then when t= 0, P= 9 and when t= 5, P= 25. Put those numbers into your formula to get two equations for C and K.
  5. Feb 3, 2006 #4
    Thanks for the replies!! It has become much clearer now.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook