Rowboat "on a Treadmill" Question

Flint · 10-02-2011, 11:51 AM

Say you are rowing a boat upstream as fast as you can. The water is flowing at 2 miles per hour, and your speed against the current is 4 miles per hour. Your rubber ducky blows off the boat, but you don’t notice. An hour later, you realize your ducky is gone. You turn around immediately and row back downstream as fast as you can. How long does it take for you to reach your ducky?

Nirvana · 10-02-2011, 01:37 PM

You don't reach the ducky ever because the rubber crocodile has eaten him

Sundae · 10-02-2011, 02:27 PM

Roosevelt was visiting.
They hadn't fed the piranhas in days.

Bye-bye ducky, bye-bye.

footfootfoot · 10-02-2011, 03:16 PM

upstream you are making 4mph against 2mph for 1 hour, so you've covered 4 miles (assuming the stream is really straight and you are measuring speed against a stationary reference, like land and not a changing reference like the water)
When you head downstream you are rowing at 6mph and the current is adding 2 mph for a total of 8mph. You would need to row for half an hour to return to the spot where your ducky fell off. An hour and a half has elapsed since the ducky fell and in that time the ducky has traveled, at 2mph, 3 more miles. You need to cover three miles to get to the ducky's current position. This will take you 22.5 minutes. in that time the ducky will have traveled another 3/4 of a mile. To close that gap and get within range you need to row for a few more minutes and use a full choke.

Gravdigr · 10-02-2011, 04:19 PM

Somebody reads "Ask Marilyn".

limey · 10-02-2011, 04:22 PM

How could you not notice the rubber ducky blowing off? He had curry for tea last night and the smell ... the smell ... and the air turned green, I mean a real vile shade of green.
Which way was the wind blowing?

infinite monkey · 10-02-2011, 04:23 PM

I read Ask Marilyn today, too.

ZenGum · 10-02-2011, 06:47 PM

Allowing a few simplifying assumptions...
no wind
uniform current
no eddies etc
The speed of the current is irrelevant since both boat and duck are in it. You've rowed away from Ducky for one hour, so to get back you must row towards him for one hour.

monster · 10-02-2011, 10:37 PM

ur such a spoilsport

sexobon · 10-03-2011, 02:00 AM

but he's got his ducks in a row

Spexxvet · 10-03-2011, 08:05 AM

How far can a duck go, in a bathtub?

Flint · 10-03-2011, 12:46 PM

I thought I was the only one that read the Parade magazine in the newspaper. I mean, besides the Readers Digest large-type crowd.

glatt · 10-03-2011, 01:13 PM

I'm a little surprised you get the dead tree edition of the paper, Flint.

I thought I was the only one who did that. I just didn't get a chance to read the paper yesterday.

lilliput1 · 10-05-2011, 11:27 PM

1.5 hours. You need to solve two equations. First: the distance the boat travels Db is 6 miles + the distance the duct travels Dd since the ducky has traveled 2 miles in an hour while the boat has traveled 4 miles in the opposite direction.
The second equation is the time of travel from the time the loss of the ducky was detected is the same for both. Since time = distance/speed, Dd/2 = Db/6. Note the boat speed downstream is 4+2 = 6 mph. Solving both equation will give the time of 1.5 hr during which the ducky has traveled 3 miles and the boat woild travel 1.5 hr x 6 mph = 9 miles (6+3).

wolf · 10-06-2011, 10:42 AM

Your first post is to do math everyone hated in elementary school. Welcome, Lilliput1. You're obviously our kind of people.

10-02-2011, 11:51 AM	#1
Flint Snowflake Join Date: Mar 2006 Location: Dystopia Posts: 13,136	Rowboat "on a Treadmill" Question Say you are rowing a boat upstream as fast as you can. The water is flowing at 2 miles per hour, and your speed against the current is 4 miles per hour. Your rubber ducky blows off the boat, but you don’t notice. An hour later, you realize your ducky is gone. You turn around immediately and row back downstream as fast as you can. How long does it take for you to reach your ducky? __________________ **************** There's a level of facility that everyone needs to accomplish, and from there it's a matter of deciding for yourself how important ultra-facility is to your expression. ... I found, like Joseph Campbell said, if you just follow whatever gives you a little joy or excitement or awe, then you're on the right track. . . . . . . . . . . . . . . . . . . . . . . . . . . Terry Bozzio**

10-02-2011, 01:37 PM	#2
Nirvana Back in 10 Join Date: Aug 2008 Posts: 3,684	You don't reach the ducky ever because the rubber crocodile has eaten him __________________ Speaking simply... do not confuse this with having a simple mind.

10-02-2011, 02:27 PM	#3
Sundae polaroid of perfection Join Date: Sep 2005 Location: West Yorkshire Posts: 24,185	Roosevelt was visiting. They hadn't fed the piranhas in days. Bye-bye ducky, bye-bye. __________________ Life's hard you know, so strike a pose on a Cadillac

10-02-2011, 03:16 PM	#4
footfootfoot To shreds, you say? Join Date: Aug 2004 Location: in the house and on the street-how many, many feet we meet! Posts: 18,449	upstream you are making 4mph against 2mph for 1 hour, so you've covered 4 miles (assuming the stream is really straight and you are measuring speed against a stationary reference, like land and not a changing reference like the water) When you head downstream you are rowing at 6mph and the current is adding 2 mph for a total of 8mph. You would need to row for half an hour to return to the spot where your ducky fell off. An hour and a half has elapsed since the ducky fell and in that time the ducky has traveled, at 2mph, 3 more miles. You need to cover three miles to get to the ducky's current position. This will take you 22.5 minutes. in that time the ducky will have traveled another 3/4 of a mile. To close that gap and get within range you need to row for a few more minutes and use a full choke. __________________ The internet is a hateful stew of vomit you can never take completely seriously. - Her Fobs

10-02-2011, 04:19 PM	#5
Gravdigr The Un-Tuckian Join Date: Apr 2007 Location: South Central...KY that is Posts: 39,517	Somebody reads "Ask Marilyn". __________________ These statements have not been evaluated by the FDA, EPA, FBI, DEA, CDC, or FDIC. These statements are not intended to diagnose, cause, treat, cure, or prevent any disease. If you feel you have been harmed/offended by, or, disagree with any of the above statements or images, please feel free to fuck right off.

10-02-2011, 04:22 PM	#6
limey Encroaching on your decrees Join Date: Feb 2004 Location: An island within the south-west coast of Scotland Posts: 7,016	How could you not notice the rubber ducky blowing off? He had curry for tea last night and the smell ... the smell ... and the air turned green, I mean a real vile shade of green. Which way was the wind blowing? __________________ Living it up on the edge ... of civilisation, within the southwest coast of

10-02-2011, 04:23 PM	#7
infinite monkey Person who doesn't update the user title Join Date: Mar 2011 Posts: 13,002	I read Ask Marilyn today, too.

10-02-2011, 06:47 PM	#8
ZenGum Doctor Wtf Join Date: Oct 2007 Location: Badelaide, Baustralia Posts: 12,861	Allowing a few simplifying assumptions... no wind uniform current no eddies etc The speed of the current is irrelevant since both boat and duck are in it. You've rowed away from Ducky for one hour, so to get back you must row towards him for one hour. __________________ Shut up and hug. MoreThanPretty, Nov 5, 2008. Just because I'm nominally polite, does not make me a pussy. Sundae Girl.

10-02-2011, 10:37 PM	#9
monster I hear them call the tide Join Date: Dec 2005 Location: Perpetual Chaos Posts: 30,852	ur such a spoilsport __________________ The most difficult thing is the decision to act, the rest is merely tenacity Amelia Earhart

10-03-2011, 02:00 AM	#10
sexobon I love it when a plan comes together. Join Date: Oct 2009 Posts: 9,793	but he's got his ducks in a row

10-03-2011, 08:05 AM	#11
Spexxvet Makes some feel uncomfortable Join Date: Dec 2005 Posts: 10,346	How far can a duck go, in a bathtub? __________________ "I'm certainly free, nay compelled, to spread the gospel of Spex. " - xoxoxoBruce

10-03-2011, 12:46 PM	#12
Flint Snowflake Join Date: Mar 2006 Location: Dystopia Posts: 13,136	I thought I was the only one that read the Parade magazine in the newspaper. I mean, besides the Readers Digest large-type crowd. __________________ **************** There's a level of facility that everyone needs to accomplish, and from there it's a matter of deciding for yourself how important ultra-facility is to your expression. ... I found, like Joseph Campbell said, if you just follow whatever gives you a little joy or excitement or awe, then you're on the right track. . . . . . . . . . . . . . . . . . . . . . . . . . . Terry Bozzio**

10-03-2011, 01:13 PM	#13
glatt ™ Join Date: Jul 2003 Location: Arlington, VA Posts: 27,717	I'm a little surprised you get the dead tree edition of the paper, Flint. I thought I was the only one who did that. I just didn't get a chance to read the paper yesterday.

10-05-2011, 11:27 PM	#14
lilliput1 Person Who Has Posted Join Date: Oct 2011 Posts: 2	1.5 hours. You need to solve two equations. First: the distance the boat travels Db is 6 miles + the distance the duct travels Dd since the ducky has traveled 2 miles in an hour while the boat has traveled 4 miles in the opposite direction. The second equation is the time of travel from the time the loss of the ducky was detected is the same for both. Since time = distance/speed, Dd/2 = Db/6. Note the boat speed downstream is 4+2 = 6 mph. Solving both equation will give the time of 1.5 hr during which the ducky has traveled 3 miles and the boat woild travel 1.5 hr x 6 mph = 9 miles (6+3).

10-06-2011, 10:42 AM	#15
wolf lobber of scimitars Join Date: Jul 2001 Location: Phila Burbs Posts: 20,774	Your first post is to do math everyone hated in elementary school. Welcome, Lilliput1. You're obviously our kind of people. __________________ wolf eht htiw og "Conspiracies are the norm, not the exception." --G. Edward Griffin The Creature from Jekyll Island High Priestess of the Church of the Whale Penis

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