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Average Thrust Force

  1. Jul 22, 2009 #1
    1. The problem statement, all variables and given/known data

    The take-off speed of a given airplane is 250 mi/h. If the take-off weight is 110,000 Kg, what is average the thrust force exerted by the engines?

    2. Relevant equations

    w=mg ,F=ma , F=mW

    3. The attempt at a solution

    the mi/h confuses me and I dont know which formula to use and is the average thrust force the net force?
  2. jcsd
  3. Jul 23, 2009 #2
    mi/h is miles per hour. Think of it as distance/time, ie, velocity.

    W(eight) is a force; it is your mass multiplied by the acceleration of the body you are standing on. On this case it is earth; so acceleration due to g(ravity) = 9.81 m/s.

    I hope it is clear then that the Weight force F = mW of the aircraft is

    9.81 * 110000 = 1,079,100 N, or 1079 kN.

    Which I am pretty sure must be the answer...but to be honest the question is rather poorly written. Is that how it appears at in the textbook/whatever? Planes don't take off vertically because of the horizontal force applied by the Engines, as you probably well already know...

    Let me know if there's anything you didn't get or would like clearing up:)
  4. Jul 23, 2009 #3
    where does the 250 miles per hour come into the formula though? or it doesnt ?
  5. Jul 23, 2009 #4


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    Homework Helper

    I suspect that you left out some info? Perhaps the length of the runway?

    And this certainly is a poorly worded question. For instance, kg is a unit of mass, not weight. If this is verbatim out of your physics book, then I feel sorry for you, and I hope we can be of some service.
  6. Jul 23, 2009 #5
    It doesn't seem to at all. This is rather common in physics questions; give you quantities you don't need to confuse you. But with that question it really is hard to tell what on earth they're asking.

    Can I ask; are you doing this for school, or self-study? If the latter I'd be happy to recommend a good textbook.
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