Results 1 to 3 of 3

Math Help - Quadratic word problem

  1. #1
    Junior Member
    Joined
    Jan 2009
    Posts
    34

    Quadratic word problem

    The distance, d (in metres), which an object travels. is given by the equation d=ut-8t^2 where u is the initial velocity (in metres per second) and t is the time in seconds it has been travelling. Show that there is only one value for t when u^2 =32d

    I'm having real trouble solving this equation for t using any algebraic method that I've learnt for quadratic equations.
    I can't figure out how to put it into the quadratic formula simply for the fact that i can't get any of the variables by themself on either side of the equation to set as x.

    The steps I've tried so far in order to rearrange for t are:
    d=ut-8t^2
    add 8t^2 to both sides
    d+8t^2=ut
    divide both sides by t
    d/t+8t=u
    take d/t away from both sides
    8t=u-d/t
    and here is where i lose track, because i figure out that i can't rearrange for t at all. i've considered converting d/t into V (final velocity) but i can't see that helping much.
    Any suggestions would be much appreciated.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Member
    Joined
    May 2006
    Posts
    244
    Quote Originally Posted by mattty View Post
    The distance, d (in metres), which an object travels. is given by the equation d=ut-8t^2 where u is the initial velocity (in metres per second) and t is the time in seconds it has been travelling. Show that there is only one value for t when u^2 =32d

    .
    Rearrange the expression for d:

     <br />
8t^2-ut+d=0<br />

    This is an equation relating t,\ u and d .

    If for some particular d and u we wish to solve for t we will use the quadratic formula. Now the discriminant for the quadratic is:

     <br />
D=u^2-32d<br />

    and it is well known that we have no real roots for t if D<0, two real roots if D>0, and exactly one real root if D=0.

    The last condition above is the one applicable here.

    .
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Jan 2009
    Posts
    34
    Many thanks for this, apparently maths at 3am isn't my strong point
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. I need help with quadratic word problem
    Posted in the Algebra Forum
    Replies: 3
    Last Post: December 1st 2009, 12:09 AM
  2. Quadratic Word Problem Help
    Posted in the Algebra Forum
    Replies: 7
    Last Post: March 28th 2009, 11:38 AM
  3. quadratic word problem :O
    Posted in the Algebra Forum
    Replies: 2
    Last Post: November 25th 2008, 08:00 AM
  4. quadratic word problem
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: November 14th 2008, 07:13 AM
  5. Quadratic Word Problem
    Posted in the Algebra Forum
    Replies: 1
    Last Post: June 8th 2006, 04:01 PM

Search Tags


/mathhelpforum @mathhelpforum