Alright, I spent the first 20 years of my life less than a mile away
from this thing, let's see...
Method 1, lets say a chunk of the river is roughly 1/2 mile across, and
the average depth is 5 ft. If we look at a slice of that river roughly 5
ft thick that would be a volume of around 66,000 cubic feet. Let's say
the river moves on average 5 to 10 miles per hour. That would mean it
moved 39,600 feet per hour, so about 7,920 slices would pass through new
Orleans each hour. 8760 hours in a year (we're approximating right?),
so that would be 4.5 X 10^12 cu ft per year.
Method 2, I live in Iowa, let's say the average rainfall is about 70
inches (should've paid better attention in Earth Science) per year, Iowa
has a surface area of approximately 4.8x10^12 square feet, fill that 70
inches deep and we're looking at 2.8x10^13 cubic feet of water landing
on Iowa per year. There are what, maybe 16 other states that drain into
the Mississippi (should've paid better attention in geography), so take
the rain from Iowa times sixteen (most of the other states are larger,
but we're just approximating) and you end up with 4X10^14 cu. Ft.
So I'm differing by a couple orders of magnitude, but estimate #2 didn't
account for evaporation, or holding ponds, or bottled water from
Wisconsin sold in New York City, etc.
When do I get my prize (or find out that I should've paid better
attention in math class!)
Cheers,
Matt
"An expert is a man who has made all the mistakes which can be made in a
very narrow field."
- Niels Bohr
-----Original Message-----
From: Forum for Physics Educators [mailto:PHYS-L@list1.ucc.nau.edu] On
Behalf Of John Denker
Sent: Friday, April 08, 2005 12:16 PM
To: PHYS-L@LISTS.NAU.EDU
Subject: Mississippi puzzle
1) How much water flows down the Mississippi (at, say, New Orleans)
in a year, approximately? Don't look anything up. Just estimate
whatever raw data you need.
-- Arno Penzias, when he was in charge of all research at Bell
Labs, liked to spring this question on members of the technical
staff. Woe betide the person who blurted out "I have no idea".
Arno would yell back "you must have SOME idea ... don't tell me
you have no idea ... FIGURE IT OUT."
-- Anybody with a US high-school education "should" be able to
answer this _without_ looking anything up. It just requires
strength of character, i.e. not giving up in the face of a
problem that seems hard. It also requires marshalling lots
of facts that may not, at first glance, have seemed relevant.
2) Find a second independent solution to the Mississippi problem.
-- Somehow knowledge of the first solution is a psychological
impediment to finding the second solution.
-- OTOH if you can reach the same conclusion by two different
avenues, it greatly increases the reliability of the result.
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