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Speed/Distance/Time + Fuel Consumption

  1. May 14, 2015 #1
    1. The problem statement, all variables and given/known data
    Distance = Speed / Time
    Speed = Distance / Time
    Distance = Speed * Time

    Also breaking up "chunks of time" in an hour

    2 of 30 mins
    3 of 20 mins
    4 of 15 mins
    5 of 12 mins
    10 of 6 mins
    12 of 5 mins
    15 of 4 mins
    20 of 3 mins
    30 of 2 mins

    2. Relevant equations
    1) An example of an easy question to do mentally would be:

    Speed of 24 mph, how far would you travel in 1 hour 15 minutes?

    2) You travel 111 miles. How much fuel will you need if you burn 36 kgs per hour, and are travelling at 148 mph?
    -Need help finding the quickest way to solve.

    3. The attempt at a solution
    0.25 of 24 is 6. Therefore, 24+6 = 30 miles



    I'm wondering if anyone knows the quickest most efficient way to solving questions such as:

    What speed covers 18 miles in 54 minutes

    And if there's a simple way to do it mentally?

    I appreciate your replies!

    This site has some sample tests including the fuel consumption questions too.
    http://www.speeddistancetime.info
     
    Last edited: May 14, 2015
  2. jcsd
  3. May 14, 2015 #2
    I don't see any way around cutting the hour into a minute value.

    1/60 = 0.1667 (Or however precise you need it.)

    Then, multiply the total time by that value:

    0.01667*54 = 0.9

    Finally, you divide your distance by your total time - as per V=D/T

    18 miles / 0.9 = 20mph

    Once you can easily figure out the solutions to distance, velocity, and time, then the rest falls into place. Fuel consumption becomes something to be multiplied into your final answer. It's all about breaking the problem down into its component parts. :)

    Also - If you're doing homework, it's probably best to get use to working the problems out the long way; and to the desired precision. You'll be thankful later on when you start solving for more complex problems.
     
  4. May 14, 2015 #3

    No this isn't for homework it's for an air crew test for the Air Force, I forgot to mention that in the post! I'm just trying to prepare for in case they have some more complex questions that they want you to do mentally. Being quick either way whether I'm writing it out or doing it mentally is what I'm looking here for!
     
  5. May 15, 2015 #4
    Ah, makes sense!

    I would think the thing to find out is how precise your answers need to be. Whether calculations are calculated loosely, and then rounded up for quick mental calculation; or whether they want you to round intermediate to thousandths and then final answers to tenths, etc. Armed with that information, you can then devise a quick way to calculate it based on your own needs. (If even possible. I know I don't have the train of thought to handle multiple numbers to three decimal places in my head!)

    Also, it might not hurt to learn conversions. I've had questions in classes given before that want you to convert before calculating. Say, they want you to find km/h, but give you a distance in miles to work with; you would first have to convert the miles into kilometers before solving. That may be an overcomplication of the problem, but it seems like they always try to throw a curve ball into the mix somewhere!

    Mind you, I'm in no way claiming to be any sort of expert here! My experience with physics has been in courses directed towards engineering, so my 46.5678 pounds of fuel may be the equivalent of 47 pounds of fuel in a real world application. Maybe someone with a little more experience will come along and be able to give a definitive answer.
     
  6. May 15, 2015 #5

    SammyS

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    For What speed covers 18 miles in 54 minutes :

    You are 6 minutes short of 1 hour.

    How far would you go in that extra 6 minutes?

    54 divided by 6 is 9.

    18 divided by 9 is 2, so you would go 2 more miles in the extra 6 minutes.

    20 mph.
     
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