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Homework Help: Quick Easy question

  1. Nov 11, 2004 #1
    Hi again.. Heres the question can someone give me a formula to solve these thanks.

    An aeroplane of mass 600kg takes off from rest in 50secs over a distance of 1500m
    a) calculate i) its speed when it lifts off
    ii) its acceleration during take-off
    iii) the force needed to produce this acceleration

    Thanks in advance
  2. jcsd
  3. Nov 11, 2004 #2


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    You should solve part ii, first.

    You know your initial velocity and position (both 0).
    You know your final position.
    You know your time.

    You also know the mass of the plane (you need this to solve part iii).

    While you don't have an equation that solves for accleration, you do have an equation that solves for final position if you already knew acceleration. You can rearrange the equation to solve for acceleration.

    Finding your acceleration gives you enough info to find your final velocity and the force required to accelerate the airplane.
  4. Nov 11, 2004 #3


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    Turkish, what do you think is the right formula ? Any guesses ?
  5. Nov 11, 2004 #4
    Bob, I don't agree that one should solve part ii, first. I think it's ok to solve part i first, but I could be wrong, because it has been a few years since I've taken physics.

    Average velocity (AV) when initial velocity (IV) = 0 is half final velocity (FV), and AV = (change in) x / (change in) t

    If you want to solve ii first, use (change in) x = IV*t + .5*a*t^2 and then for i use FV = IV + a*t.
    Last edited: Nov 11, 2004
  6. Nov 11, 2004 #5


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    philosophking, 2 things :

    1. We do not do other people's homework for them. That would be counterproductive, besides being unethical. We try to help by provoking thought or giving suggestions. We expect the student to have put in an effort before coming here. Please read the "sticky" at the top of this forum.

    2. While I agree that your approach will work just as well as BobG's, I'd like to point out that you have a typo in your formula for the average velocity.

    It's not too late to edit your post to conform to guidelines.
  7. Nov 12, 2004 #6
    I think there should be no problem for diligent,bright students.
    You are able to solve these questions.
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