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Homework Help: Iv'e got every value except velocity initial and acceleration. help ?

  1. Sep 11, 2010 #1
    1. The problem statement, all variables and given/known data

    An accelerating lab cart passes through two photo gate timers 3.0 m apart in 4.2 s. The velocity of the cart at the second timer is 1.2 m/s (4 marks)

    a.) What is the cart’s velocity at the first gate?

    b.) What is the acceleration?

    2. Relevant equations

    v = vi + at
    Vaverage = d/t
    d = vi(t) + 0.5 at^2
    Vf^2 = Vi^2 + 2ad

    3. The attempt at a solution

    d = 3m
    t = 4.2 seconds
    vf = 1.2 m/s
    vi = ?
    a = ?

    I have tried all of those formulas and they have at least 2 unknowns afterwards.

    The question is worth 4 marks so velocity initial can't be 0.
  2. jcsd
  3. Sep 11, 2010 #2
    posted in error.
  4. Sep 11, 2010 #3
    Does that mean this question is invalid?

    And if so should I write this as my answer and just hand it in?
  5. Sep 12, 2010 #4
    No, it means what I'd posted didn't address your problem, and having submitted I couldn't just delete the whole thing. Sorry for being ambiguous

    See if you can find this formula in your book: For uniform acceleration Vavg = (Vf + Vi)/2.

    From that and what you've already got, you can get Vi, which lets you get a.
    Last edited: Sep 12, 2010
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