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Projectile motion problem

  1. Feb 1, 2009 #1
    1. The problem statement, all variables and given/known data

    A particle leaves its initial position x_0 at time t=0 moving in the positive x direction with speed v_0 but undergoing acceleration of magnitude a in the negative x direction. Find expressions for (a) the time when it returns to the position x_0.

    2. Relevant equations

    v=v_0-at
    x=x_0+v_0*t

    3. The attempt at a solution

    i know that v=v_0, but that gives me a time of 0, which doesn't make sense. i'm also not supposed to use x_0 in the solution. otherwise, i think the solution should be (v-v_0)/-a.
     
  2. jcsd
  3. Feb 1, 2009 #2

    Delphi51

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    Homework Helper

    This formula is for uniform motion (zero acceleration).
    You need to use x = Vo*t + .5*a*t^2.
    When you set x = 0, you will have a quadratic equation with two solutions. One will be t=0 of course and the other greater than zero.
     
  4. Feb 1, 2009 #3

    Mk

    User Avatar

    By the way estie, if you wish to use TeX-style notation on this forum you can wrap [ tex] [/tex] tags around your equations so it'll look more like this:
    [tex]x=x_0+v_{0}t
    [/tex]

    Welcome to PF!
     
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