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Relative Motion- Airplane/Wind

by revults
Tags: airplane or wind, motion, relative
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revults
#1
Feb13-13, 11:27 AM
P: 10
1. The problem statement, all variables and given/known data

A jetliner has a cruising air speed of 620mph relative to the air.

Part B
How long does it take this plane to fly round-trip from San Francisco to Chicago, an east–west flight of 2000 miles each way, if the wind is blowing at 120mph from the west to the east?




2. Relevant equations



3. The attempt at a solution

I've tried 8 hours.
and 7.225 hours.
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tms
#2
Feb13-13, 11:37 AM
P: 616
Show us your work, or we can't tell where, if anywhere, you went astray.
revults
#3
Feb13-13, 11:40 AM
P: 10
i did

620-120= 500

so that makes 4000/500= 8 hours


for 1 other

it only affects 1 trip

so 2000/620= 3.225

2000/500= 4

so trip time = 7.225

both answers wrong

tms
#4
Feb13-13, 11:44 AM
P: 616
Relative Motion- Airplane/Wind

The wind affects the trip in both directions: it helps in one direction and opposes in the other.
revults
#5
Feb13-13, 11:45 AM
P: 10
620 + 120 one-way = 740
620 - 120 one-way = 500

2000/740 mph = 2.70
2000/500 mph = 4



= 6.7 hours


is that correct
BruceW
#6
Feb13-13, 11:46 AM
HW Helper
BruceW's Avatar
P: 3,440
hi there, welcome to physicsforums. I'm guessing your assumption is that the wind velocity and cruising velocity 'add up' to get the true speed. Since they don't give you any other information, then this does seem like the right way to do it.

I get a different answer to you though. Remember that since he is doing a two-way flight, that on the way there, the plane is going against the wind, and with the wind on the way back.

EDIT: lol, I only saw your first post when I wrote this. And yes, I also get an answer of 6.7 hours
revults
#7
Feb13-13, 11:47 AM
P: 10
Quote Quote by BruceW View Post
hi there, welcome to physicsforums. I'm guessing your assumption is that the wind velocity and cruising velocity 'add up' to get the true speed. Since they don't give you any other information, then this does seem like the right way to do it.

I get a different answer to you though. Remember that since he is doing a two-way flight, that on the way there, the plane is going against the wind, and with the wind on the way back.

I posted some new work, is that what you got?
BruceW
#8
Feb13-13, 11:48 AM
HW Helper
BruceW's Avatar
P: 3,440
yep! nice work :)


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