Results 1 to 2 of 2

Math Help - exponential functions

  1. #1
    Junior Member
    Joined
    Dec 2006
    Posts
    60

    exponential functions

    A man jumps from above - his speed of descent is given by V = 50(1-2^-0.2t) m/s where t is the time in seconds. Find the time taken for his speed to reach 40 m/s.

    I know to set the equation to:

    40 = 50(1 - 2^-0.2t)

    but i can't seem to carry it out from there..because i can't take the log of both sides when the numbers are negative.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Junior Member
    Joined
    Feb 2006
    From
    United Kingdom
    Posts
    70
    rearrange it to get the 2^{-0.2t} by itself.. eg:

    40 = 50(1-2^{-0.2t})
    =>
    40 = 50 - 50*2^{-0.2t}
    =>
    -10 = -50*2^{-0.2t}
    =>
    1/5 = 2^{-0.2t}

    then take logs of both side and continue. you should get something like t = 5 \frac{\log{5}}{\log{2}}
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 2
    Last Post: June 9th 2011, 09:54 AM
  2. log and exponential functions
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: May 3rd 2009, 03:27 PM
  3. Exponential Functions
    Posted in the Pre-Calculus Forum
    Replies: 4
    Last Post: October 16th 2008, 09:28 PM
  4. Exponential Functions...
    Posted in the Pre-Calculus Forum
    Replies: 8
    Last Post: August 26th 2008, 09:51 AM
  5. exponential functions
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: March 25th 2008, 08:55 AM

Search Tags


/mathhelpforum @mathhelpforum