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Old September 11th, 2006, 03:39 AM   #1
arthurracoon
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Physics Help!


I have a hw due today at 1pm


this is the last problem on the assignment...some help?

City A lies directly west of city B. When there is no wind, an airliner makes the round trip flight of distance s between them in a flight time of t1 while traveling at the same speed in both directions. When a strong, steady wind is blowing from west to east and the airliner has the same air speed as before, the round trip takes a flight time of t2.

How fast is the wind?
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Old September 11th, 2006, 03:40 AM   #2
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I have the velocity when theres no wind: v = 2s/t1
i think i also have the avg velocity when there is wind: Vavg = s/t2
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Old September 11th, 2006, 06:43 AM   #3
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Old September 11th, 2006, 07:21 AM   #4
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Is this an African or European flight?
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Old September 11th, 2006, 07:25 AM   #5
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I just forwarded this thread to your instructor for cheating....
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Old September 11th, 2006, 07:25 AM   #6
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Old September 11th, 2006, 08:42 AM   #7
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Arthur, you know the following:
t1=s/v+s/v=2s/v
t2=s/(v+w)+s/(v-w)
v=2s/t1

s, t1, t2, and v are all known. All that's left is to do the algebra (and make sure everything is in terms of s, t1, and t2). You have to multiply those fractions in the t2 equation by (v-w)/(v-w) and (v+w)/(v+w) respectively to get a common denominator (v^2-w^2). The rest I'll leave up to you.
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Old September 11th, 2006, 09:43 AM   #8
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Quote:
Originally Posted by nm132
Arthur, you know the following:
t1=s/v+s/v=2s/v
t2=s/(v+w)+s/(v-w)
v=2s/t1

s, t1, t2, and v are all known. All that's left is to do the algebra (and make sure everything is in terms of s, t1, and t2). You have to multiply those fractions in the t2 equation by (v-w)/(v-w) and (v+w)/(v+w) respectively to get a common denominator (v^2-w^2). The rest I'll leave up to you.
ok

so i get:

t2 = 2vs/(v^2-w^2)

then i solve for w to get (and i plug in 2s/t1 for v):

w = sqrt(v^2 - 2vs/t2)

is this correct? because the online program says its not.
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Old September 11th, 2006, 10:35 AM   #9
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You have to plug stuff into an online program? That sucks. If it asks for a solution involving algebra is it able to discriminate between different ways you can write the answer?

Yeah I think that answer is right. That's what I got for w, with it simplifying to the form: w=2s/t1*sqrt(1-t1/t2)
which passes the sanity check of t1=t2 -> w=0.

Maybe there's something we're missing but everything seems right to me.
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Old September 11th, 2006, 10:54 AM   #10
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Yeah I was a Sociology/Criminology major in college... sorry Arthur.

But good luck!
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Old September 11th, 2006, 11:03 AM   #11
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Quote:
Originally Posted by nm132
You have to plug stuff into an online program? That sucks. If it asks for a solution involving algebra is it able to discriminate between different ways you can write the answer?

Yeah I think that answer is right. That's what I got for w, with it simplifying to the form: w=2s/t1*sqrt(1-t1/t2)
which passes the sanity check of t1=t2 -> w=0.

Maybe there's something we're missing but everything seems right to me.
yup

it sucks

it said i was off by a multiplicative factor....

stupid masteringphsics.com....
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Old September 11th, 2006, 11:16 AM   #12
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Quote:
Originally Posted by nm132
You have to plug stuff into an online program? That sucks. If it asks for a solution involving algebra is it able to discriminate between different ways you can write the answer?

Yeah I think that answer is right. That's what I got for w, with it simplifying to the form: w=2s/t1*sqrt(1-t1/t2)
which passes the sanity check of t1=t2 -> w=0.

Maybe there's something we're missing but everything seems right to me.
i think it plugs in numbers to check

i entered both forms of the solution (simplified and unsimplified)...wrong both times

i hate doing physics on a computer...
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Old September 11th, 2006, 11:22 AM   #13
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wow...im an idiot.

s is the round trip distance...not one way...
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Old September 11th, 2006, 11:36 AM   #14
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Quote:
Originally Posted by arthurracoon
wow...im an idiot.

s is the round trip distance...not one way...
yup...i got it...

thanks nm132!

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Old September 11th, 2006, 11:43 AM   #15
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Quote:
Originally Posted by arthurracoon
wow...im an idiot.
Me too. I was reading your post about it telling you that you were off my a multiplicative factor and then realized what the issue was.
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