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Homework Help: Force and distance

  1. Sep 17, 2006 #1
    In a grocery store, you push a 13.5 kg shopping cart with a force of 12.5 N. If the cart starts at rest, how far does it move in 3.00 s?

    Here's what I did:
    m=13.5 kg
    f=12.5 N
    t=3s
    v(i)=0
    F=ma
    a=f/m
    12.5/13.5=0.93m/s^2=accel.
    V(final)=0+at= 0+(.93)(3)=2.79
    Vf^2=Vi^2+2a(deltax)= solve for change in X= (2a)Vf^2 (Vf = final velocity, Vi= initial velocity)
    so, (2)(.93)*(2.79)^2= 14.5 m.
    Ok, so what did I do wrong? I can't figure it out.....
     
  2. jcsd
  3. Sep 17, 2006 #2

    Hootenanny

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    Staff Emeritus
    Science Advisor
    Gold Member

    Here's your problem, you've just made a mistake on your manipulation;

    [tex]v_{f}^{2} = v_{i}^{2} + 2ax \Rightarrow x = \frac{v_{f}^{2}}{2a}[/tex]

    Also, becareful of inducing rounding errors.
     
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