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Homework Help: Acceleration and velocity

  1. Oct 22, 2008 #1
    1. The problem statement, all variables and given/known data
    A plane is moving at 270 m/s accelerates at 28 m/s ^2 for 9.8s. How far would it have traveled in the time.

    using vi + a(t) i was able to get its final velocity 544.4m/s but when i multiply it by 9.8s it tells me that is wrong what am i doing wrong? thanks
  2. jcsd
  3. Oct 22, 2008 #2
    For what length of time does the plane travel at a speed of 544.4 m/s?
  4. Oct 22, 2008 #3
    9.8s but when i multiply it by 544.4 m /s its wrong??
  5. Oct 22, 2008 #4
    What speed did the plane have at the start of the 9.8s? Try doing a before and after sketch with the plane's speed labelled each time.
  6. Oct 22, 2008 #5
    Iam still confused lol
  7. Oct 22, 2008 #6
    a. What speed was the plane going at right at the start of the question?

    b. What speed was the plane going at right at the end of the question, 9.8 s later?

    c. What do you think it was doing in between :-)

    (Once you've got that conceptually, you can start to think about distance. If you just plug and chug with an equation for the distance right now, you'll be confused about a lot of things later in your course.)
  8. Oct 22, 2008 #7
    I got it man !!!!! woot.
    Here it is d = Vi(t)+1/2a(t)^2
    therefore 270(9.8) + 1/2(28)(9.8)^2
    = 3990.56 m
    THANKS heth
  9. Oct 23, 2008 #8
    Nice one! The key is realising that the plane's velocity is changing all the time, so you can't use an equation that assumes the velocity is constant.
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