Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Is it right

  1. Jan 24, 2005 #1
    A 747 airliner reaches its takeoff speed of 173 mi/h in 35.2s. What is the magnitude of its average acceleration?

    (77.3341 m/s)/(35.2 s) = 2.20 m/s^2

    I am wondering did I do it correctly?
  2. jcsd
  3. Jan 24, 2005 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Except for the transformation from miles to meter, you sure did! And by "except", I don't mean that your transformation is wrong, I only mean that I don't know how to do the transformation, so I can't verify it. But the important part is that you used the right concept, that is,

    [tex]a_{av} = \frac{\Delta v}{\Delta t}[/tex]

    and did not forget yo convert the units of time so they match.
  4. Jan 25, 2005 #3
    what means "correctly"?

    please clarify what you mean by that?
    getting the right answer and "doing it correctly" are very different things. did your teacher/instructor/whatever want to see all of the steps involved? if so, your answer may be right but the "doing it" is invisible and can't be judged! :wink:

    the "process" might be something like this:

    ((173 mi/hr)*(# ft/mile)*(#m/ft)*(1 hour/60min)*(1min/60 s))/35.2 s.

    if i got all of the conversions in there and all of the units cancel right, the answer will be right for acceleration = delta v / delta t.

    did that make sense?
  5. Jan 25, 2005 #4


    User Avatar
    Science Advisor
    Homework Helper

    [tex] 1Mph=\frac{1609.344}{3600}ms^{-1} [/tex]

  6. Feb 1, 2005 #5
    ok, i'll bite........

    if the problem is stated in miles/hour and seconds for acceleration, what was the purpose of converting to meters/second? was that required by the problem, or are all problems' answers required to me in the metric system?

  7. Feb 1, 2005 #6


    User Avatar
    Science Advisor
    Homework Helper

    Of course not...But in this case it would be rather awkward to express the acceleration in [itex] M hr^{-2} [/itex],don't u think...?

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook