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I got a question

  1. Feb 7, 2005 #1
    A plane landing on a small tropical island has
    just 66 m of runway on which to stop.
    If its intial speed is 58 m/s, what is the
    maximum acceleration of the plane during
    landing, assuming it to be constant? Answer
    in units of m/s^2.

    i know im supposed to use the equation v^2 = Vo^2 + 2a(x-Xo) but wht is V^2
     
  2. jcsd
  3. Feb 7, 2005 #2

    dextercioby

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    What formula would you have to use??

    Daniel.
     
  4. Feb 7, 2005 #3

    v^2 = Vo^2 + 2a(x-Xo) but wht is V^2
     
  5. Feb 7, 2005 #4

    dextercioby

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    Well,the plane has to stop,so the final velocity should be...??

    Daniel.
     
  6. Feb 7, 2005 #5

    ah ha, ok i understand
     
  7. Feb 7, 2005 #6
    follow up question

    How long does it take for the plane to stop
    with this acceleration? Answer in units of s.

    i used the equation X = Xo + Vot + 1/2at^2 is this correct?
     
  8. Feb 7, 2005 #7

    dextercioby

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    How about
    [tex] v_{fin}=v_{init}+at [/tex]

    ?? :wink:

    The one u posted is correct as well,but te one suggested by me is more direct.

    Daniel.
     
  9. Feb 7, 2005 #8

    i just got that
     
  10. Feb 7, 2005 #9
    one more question

    A car starts from rest and travels for 6.4 s with
    a uniform acceleration of 3.3 m/s^2. The driver
    then applies the brakes, causing a uniform
    acceleration of 1.5 m/s^2.
    If the brakes are applied for 2.5 s, how fast
    is the car going at the end of the braking
    period? Answer in units of m/s.

    this is what I did, i subtracted the final acceleration from the initial and the the time for braking from the total time the car was traveling. then i used the equation V = Vo + at is that what you would do?
     
  11. Feb 7, 2005 #10

    dextercioby

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    No,i would compute the velocity after 6.4 secs and then the final velocity.Do the same & it'll be okay.

    Daniel.
     
  12. Feb 7, 2005 #11
    one final add on

    same question, How far has it gone? Answer in units of m.

    i used the formula X = Xo + Vot + 1/2at^2 for each time and acceleration then i subtracted the distance i got from the deceleration from the the distance i got for the acceleration
     
  13. Feb 7, 2005 #12

    dextercioby

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    Why did u subtract them...?It doesn't go backwards... :rolleyes: :wink:

    Daniel.
     
  14. Feb 7, 2005 #13
    because one answer was negative even though distance cannot be negative( the decleration distance) and the acceleration distance was positive. am i supposed to add them?
     
  15. Feb 7, 2005 #14

    dextercioby

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    Of course,it decelerates in the same direction as it was accelerating (the velocity vector keeps direction,just the modulus varies),so they have to be added.

    Daniel.
     
  16. Feb 7, 2005 #15

    im getting 72.27meters, can u check that for me? i think its wrong
     
    Last edited: Feb 7, 2005
  17. Feb 7, 2005 #16

    dextercioby

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    Nope,should be roughly 110m...


    Daniel.
     
  18. Feb 7, 2005 #17
    plane on island

    Vf^2 = Vi^2 + 2ad

    Vf = 0. because the plane will be at stopped after it lands

    rearrange formula

    -Vi^ = 2ad

    a = (-Vi^2)/(2*d)

    a = (-58^2)/(2*66)

    a = -25.5 m/s^2

    aceleration is negative because the plane is slowing down while it lands.
     
  19. Feb 7, 2005 #18
    v2 is zero, once the plane lands it dosent have a velocity now does it
     
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