# Point of No Return (Wrd P)

• Jan 26th 2008, 08:40 PM
CODEONE
Point of No Return (Wrd P)
A plane flying the 3458-mi trip from New York City to London has a 50-mph tailwind. The flight's point of no return is the point at which the flight time required to return to New York is the same as the time required to continue to London. If the speed of the plane in still air is 360 mph, how far is New York from the point of no return?

Can anyone lead me in the right direction with this one? I've been at it for an hour and am brain dead x.x
• Jan 26th 2008, 08:58 PM
Jhevon
Quote:

Originally Posted by CODEONE
A plane flying the 3458-mi trip from New York City to London has a 50-mph tailwind. The flight's point of no return is the point at which the flight time required to return to New York is the same as the time required to continue to London. If the speed of the plane in still air is 360 mph, how far is New York from the point of no return?

Can anyone lead me in the right direction with this one? I've been at it for an hour and am brain dead x.x

the 50-mph tail wind means the plane's speed to London is $360 + 50 = 410$ mph and the plane's speed to New York is $360 - 50 = 310$ mph

let $d$ be the distance from New York to the point of no return
then $3458 - d$ is the distance from London to the point of no return.
let $t_L$ be the time to fly to London from the point of no return
let $t_{NY}$ be the time to fly to New York from the point of no return

recall that: $\mbox{Speed } = \frac {\mbox{Distance}}{\mbox{Time}} \implies \mbox{Time } = \frac {\mbox {Distance}}{\mbox{Speed}}$

so, $t_{NY} = \frac d{310}$

and $t_L = \frac {3458 - d}{410}$

since the times from the point of no return are the same, we have:

$\frac d{310} = \frac {3458 - d}{410}$

now solve for $d$
• Oct 7th 2008, 07:00 PM
MyNameisZach
Ummmmmm NO!!!
Originally Posted by CODEONE http://www.mathhelpforum.com/math-he...s/viewpost.gif
A plane flying the 3458-mi trip from New York City to London has a 50-mph tailwind. The flight's point of no return is the point at which the flight time required to return to New York is the same as the time required to continue to London. If the speed of the plane in still air is 360 mph, how far is New York from the point of no return?

Can anyone lead me in the right direction with this one? I've been at it for an hour and am brain dead x.x

the 50-mph tail wind means the plane's speed to London is http://www.mathhelpforum.com/math-he...f4ae2b2d-1.gif mph and the plane's speed to New York is http://www.mathhelpforum.com/math-he...d020e700-1.gif mph

let http://www.mathhelpforum.com/math-he...16e091ad-1.gif be the distance from New York to the point of no return
then http://www.mathhelpforum.com/math-he...6757e351-1.gif is the distance from London to the point of no return.
let http://www.mathhelpforum.com/math-he...dda7c57e-1.gif be the time to fly to London from the point of no return
let http://www.mathhelpforum.com/math-he...c447bf78-1.gif be the time to fly to New York from the point of no return

recall that: http://www.mathhelpforum.com/math-he...8146282e-1.gif

so, http://www.mathhelpforum.com/math-he...5aa77416-1.gif

and http://www.mathhelpforum.com/math-he...0e34e9c5-1.gif

since the times from the point of no return are the same, we have:

http://www.mathhelpforum.com/math-he...5d6f89ed-1.gif

now solve for http://www.mathhelpforum.com/math-he...16e091ad-1.gif

• Oct 7th 2008, 07:28 PM
Jhevon
Quote:

Originally Posted by MyNameisZach
Originally Posted by CODEONE http://www.mathhelpforum.com/math-he...s/viewpost.gif
A plane flying the 3458-mi trip from New York City to London has a 50-mph tailwind. The flight's point of no return is the point at which the flight time required to return to New York is the same as the time required to continue to London. If the speed of the plane in still air is 360 mph, how far is New York from the point of no return?

Can anyone lead me in the right direction with this one? I've been at it for an hour and am brain dead x.x

the 50-mph tail wind means the plane's speed to London is http://www.mathhelpforum.com/math-he...f4ae2b2d-1.gif mph and the plane's speed to New York is http://www.mathhelpforum.com/math-he...d020e700-1.gif mph

let http://www.mathhelpforum.com/math-he...16e091ad-1.gif be the distance from New York to the point of no return
then http://www.mathhelpforum.com/math-he...6757e351-1.gif is the distance from London to the point of no return.
let http://www.mathhelpforum.com/math-he...dda7c57e-1.gif be the time to fly to London from the point of no return
let http://www.mathhelpforum.com/math-he...c447bf78-1.gif be the time to fly to New York from the point of no return

recall that: http://www.mathhelpforum.com/math-he...8146282e-1.gif

so, http://www.mathhelpforum.com/math-he...5aa77416-1.gif

and http://www.mathhelpforum.com/math-he...0e34e9c5-1.gif

since the times from the point of no return are the same, we have:

http://www.mathhelpforum.com/math-he...5d6f89ed-1.gif

now solve for http://www.mathhelpforum.com/math-he...16e091ad-1.gif

Ummmm, YES!!!

i made no mistake, please check your algebra, Zack. my solution gives the distance is 1488.86, which is rounded to 1489, as is in the book. you solved for d incorrectly (which should have been obvious, since if you plug in that d in my equation, you have the left side positive, but the right side negative)

is there anything else you don't understand in my solution?
• Oct 7th 2008, 08:41 PM
MyNameisZach
I still don't see how you get that answer for D with your equation. I cross multiple the two equations left & continually come out with d = 10719.8 which is not the answer. Are you trying to make me look like a fool? Please show me how you get this answer i really want to know, r u a math teacher?
• Oct 7th 2008, 08:50 PM
Jhevon
Quote:

Originally Posted by MyNameisZach
I still don't see how you get that answer for D with your equation. I cross multiple the two equations left & continually come out with d = 10719.8 which is not the answer. Are you trying to make me look like a fool? Please show me how you get this answer i really want to know, r u a math teacher?

i am not a math teacher, and i don't even know you, Zach, why would i be interested in making some random guy i met on the internet look like a fool? i merely said you solved for d incorrectly. i figured you made a silly mistake and could correct it. evidently you keep making the same mistake.

there are many ways to solve the equation. for your benefit, i will use your cross-multiplication method.

$\frac d{310} = \frac {3458 - d}{410}$

cross-multiply

$\Rightarrow 410 d = 310(3458 - d)$ .............chances are you made a mistake here and did not distribute the 310 to both terms

$\Rightarrow 410 d = 1071980 - 310d$ ...........add 310d to both sides

$\Rightarrow 720d = 1071980$ ..............divide both sides by 720

$\Rightarrow d = \frac {1071980}{720}$ ..........simplify

$\Rightarrow \boxed{d = 1488.861 \approx 1489}$
• Oct 7th 2008, 10:38 PM
MyNameisZach
Suddenly i see
Omg i was making the stupidest mistake i feel like an idiot, thanks for taking the time to answer. can i message you if i have trouble in the future?
• Oct 8th 2008, 05:27 PM
Jhevon
Quote:

Originally Posted by MyNameisZach
Omg i was making the stupidest mistake i feel like an idiot, thanks for taking the time to answer. can i message you if i have trouble in the future?

it is best (for you) to post your questions here in the forum. i'll help you out if i'm around and no one else does :)
• Oct 10th 2008, 10:38 AM
MyNameisZach
<3
Thanks, i love you