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Re: Itpro.... continued.,... you'll like this!
Posted by 'itpro' on 17 Feb 2011 @ 11:33

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itproJoined: August 2001
Total Posts: 6
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My favourite demonstration of this technique is contained in a very simple, logical question....

An aircraft flies straight from point A going due-North for 100 miles to point B where it turns round and head South back to A. It's flying on a totally calm day with ZERO wind speed at exactly 100mph and thus takes 2 hours to do the round trip.

Nice and simple!

The next day, there is a 20mph Northerly wind (coming from the North). It therefore files 'slower' (over the ground) going North and then faster on the way back.

So..... does the journey on THAT day take:

More than 2 hours?
..less than 2 hours?
.... or exactly 2 hours?

Simple 'common sense' tells you that it will go North 20mph slower and South 20mph faster...i.e., the differences will even-out. Thus it LOOKS as though the journey will STILL take 2 hours. Doesn't it.....?

So.... what's your answer.....?

(think about it, decide and then scroll down.... don't CHEAT)
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The way to answer this one is to use 'Reduction ad Absurdum'.

All you need to do is to RAISE the head/tail wind to an 'absurd' speed.

OK....

How fast would the plane travel (over the ground) if the Northerly head wind was 100mph........?

Instantly, you can see that it would NEVER GET to point B as it would remain, stationary, over Point A forever!

You can then work out that if the Northerly wind speed was 99mph, then the plane would be traveling north at 1mph.... thus the Northerly journey would take 100 hours and thus we can see that ANY head-wind will make that round trip take LONGER than 2 hours no matter WHAT the speed of the wind.

It's astounding that, what is so OBVIOUS at absurd speeds (100mph) is NOT so obvious at 'sensible' speeds (20mph0.

It's fun how using something as simple as THAT piece of logic shows that our 'common sense' is easily shown to be WRONG!

Ian

Message Thread:

Site on go slow again? by 'raceinstructor' (15 Feb 2011 @ 8:16)

Re: Site on go slow again? by 'dynamax' (15 Feb 2011 @ 9:13)

Re: Site on go slow again? by 'Newshound' (15 Feb 2011 @ 9:31)

Re: Site on go slow again? by 'NickyW' (15 Feb 2011 @ 16:03)

Re: Site on go slow again? by 'PGB' (15 Feb 2011 @ 18:11)

Re: Site on go slow again? by 'itpro' (15 Feb 2011 @ 18:17)

Re: Site sorted! by 'BrianP' (15 Feb 2011 @ 18:26)

Re: Site sorted! by 'Newshound' (15 Feb 2011 @ 18:35)

Re: Site sorted! by 'chriskasch' (15 Feb 2011 @ 19:36)

Re: Site sorted! by 'BrianP' (15 Feb 2011 @ 19:50)

Re: Site sorted! by 'alanrr' (15 Feb 2011 @ 23:06)

Re: Site sorted! by 'PaulMRotax' (16 Feb 2011 @ 9:00)

Re: Site sorted! by 'itpro' (16 Feb 2011 @ 11:05)

Re: Site sorted! by 'NickyW' (16 Feb 2011 @ 12:23)

Re: Site sorted! by 'itpro' (16 Feb 2011 @ 13:00)

Re: Site sorted! by 'PaulMRotax' (16 Feb 2011 @ 18:44)

Re: Site sorted! by 'itpro' (16 Feb 2011 @ 19:57)

Re: Itpro by 'Attack2001' (16 Feb 2011 @ 20:38)

Re: Itpro by 'itpro' (17 Feb 2011 @ 11:10)

Re: Itpro.... continued.,... you'll like this! by 'itpro' << You are here!

Re: Itpro.... continued.,... you'll like this! by 'PaulMRotax' (17 Feb 2011 @ 12:46)

Re: Itpro.... continued.,... you'll like this! by 'Attack2001' (17 Feb 2011 @ 19:15)

Re: Itpro.... continued.,... you'll like this! by 'PaulMRotax' (18 Feb 2011 @ 13:04)

Re: Itpro.... continued.,... you'll like this! by 'Newshound' (18 Feb 2011 @ 13:50)

Re: Itpro.... continued.,... you'll like this! by 'PaulMRotax' (18 Feb 2011 @ 13:51)

Re: Itpro.... continued.,... you'll like this! by 'Newshound' (18 Feb 2011 @ 14:04)

Re: Itpro.... continued.,... you'll like this! by 'PaulMRotax' (18 Feb 2011 @ 14:11)

Re: Itpro.... continued.,... you'll like this! by 'Newshound' (18 Feb 2011 @ 14:16)

Re: Itpro.... continued.,... you'll like this! by 'PaulMRotax' (18 Feb 2011 @ 14:33)

Re: Site sorted! by 'PaulMRotax' (17 Feb 2011 @ 12:42)

Re: Site on go slow again? by 'kudos' (20 Feb 2011 @ 0:12)

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