Set up of applications involving uniform motion  TOPIC_SOLVED

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Set up of applications involving uniform motion

Postby ckowen on Tue Sep 01, 2009 6:49 am

this is driving me bananas.


i can do the distance=rate x time problems well enough but setting this one up has utterly baffled me. :shock: :confused:

Hazel and Emily fly from atlanta to San diego. the flight to sandiego is against the wind and takes 4 hours. the return flight with the wind takes 3.5 hours. if the speed of the wind is 40 mph find the speed of the plane in still air.


i know the table you do where you set it up but im just utterly baffled as how to set this one up to find the speed of the plane in still air. something to do with resistence...uuhhh...help?


oh and im new here. Hi! :wave:
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Postby stapel_eliz on Tue Sep 01, 2009 5:10 pm

ckowen wrote:i know the table you do where you set it up but im just utterly baffled as how to set this one up to find the speed of the plane in still air.

The "in still air" part is a fancy way of saying "what the speedometer reads" (or whatever they call it in a passenger plane). The speedometer reading and the actual speed are not necessarily the same thing. For instance, if your car is stuck on ice, your speedometer might be reading "60", while the car is actually slowly drifting backwards. Or think of trying to row a boat up a waterfall: you can row like crazy, but you ain't goin' up! :wink:

So the secret here is to account for the two input speeds with result in the one output speed: the speedometer reading for the plane, and the wind. On their trip out, the wind is against them, pushing them back, and thus subtracting from what the plane's engines are doing. On their trip back, the wind with with them, pushing them forward, and thus adding to what the plane's engines are doing.

Once you set up the "rate" part of your table with this information, use the fact that, whatever the distance was, it was the same in each direction. Set the "rt" expressions equal, and solve for the reading of the plane's speedometer. :D
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