1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
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: Finding initial speed and accleration

  1. Sep 2, 2007 #1
    1. A truck covers 50.0 m in 9.00 s while smoothly slowing down to final speed 2.40 m/s.

    Find the trucks original speed.

    Find its accleration.

    2. Relevant equations
    im using
    x = v0*t + 1/2 *a*t2
    v2 = v02 + 2*a*x

    I believe this is what the question gives me.

    Xo = 0
    Xf = 50
    Vo = ?
    Vf = 2.4
    a = ?
    t = 9 secs

    3. im positive that i have to use the two equations stated above. but both equations have accleration and Vo as unknown variables. i just need a hint on whats the best way to find accleration or Vo. I dont know if im clear what im saying but its the best way i can explain it. sorry.
  2. jcsd
  3. Sep 2, 2007 #2
    Hm...ok I tried the problem (I suck @ sig figs hope you're better @ them).

    first your formula's are wrongish:

    [tex]x=x_0+v_0 t+\frac{1}{2}at^2[/tex]

    you could easily use the 2n'd formula to find a but you don't know initial v.

    So use the first formula, since you're given begining/ending position and ending speed.
    But you need to solve for initial v first. even though you don't know it you know that v=v0+at so move the variable's on the 2n'd formula to solve for initial v, plug that into the first and solve for a, and go from there.
  4. Sep 2, 2007 #3
    thanks. worked them to get right answer. silly mistake using wrong equations.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook