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How far has it traveled in this time?

  1. Sep 10, 2006 #1
    I need help on this one hw problem.

    A 747 jetliner lands and begins to slow to a stop as it moves along the runway. If its mass is 3.50 x 10^5 kg, its speed is 27.0 m/s, and the net breaking force is 4.30 x 10^5 N,

    a) what is it speed 7.50s later
    b) How far has it traveled in this time?

    I don't know what equation or formula to use. I also don't know how to relate the force into the problem. The only thing that I know is the accerleration is zero because the jet is breaking.

    Can someone please help me on what equation I should use to slove for the answer,
  2. jcsd
  3. Sep 10, 2006 #2

    Chi Meson

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    And the "only thing you know" is very wrong.

    The acceleration is not zero. If acceleration were zero, then the jet would maintain a constant velocity.

    Do you have the mass of the jet? Do you have the "net force" on the jet? (Yes you do). Does "Newton's Second Law of Motion" ring a bell?
  4. Sep 10, 2006 #3
    ok so
    the accerleration= 1.22 m/s square

    can I use
    (x=finial y postion) = (Xo=initial y postion) + (Vox= initial velocity of X component)(t=time) + 1/2(a=accerleration)(t=time)square

    X = Xo + Voxt + 1/2 a t^2

    Can I use this to find where the jet is at 7.5 second later?
  5. Sep 10, 2006 #4
    Newton's Second Law is F=ma, hence a=m/F, giving a value of 0.81m/s squared in this case.
    Now you can use v=u+at for part a) where u=27m/s, a=0.81 and t=7.5.
    For part b) you could use the formula s=ut+0.5a(t^2). Hope that helps.
  6. Sep 10, 2006 #5
    Oops sorry your acceleration value is correct, my mistake. Everything else should be ok, sorry.
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