A woman who weighs 100 lb carries two gold balls, 10 lb each.

physics/juggling.bridge New

New entry, edited from material collected for the archive and not yet in a released version.

Problem

A woman who weighs 100 lb carries two gold balls, 10 lb each.  She has
to cross a bridge over a deep ravine, and the maximum weight the bridge
can hold is exactly 112 lb.  The bridge is too long for her to throw or
roll a ball over it, and she cannot leave one ball on one side while
carrying the other across (bystanders would immediately steal a ball
left unattended).  A puzzle book says she got across by juggling the
balls.  Does juggling really keep the load on the bridge under 112 lb?
[ Editor: problem statement reconstructed from the posting, which
quotes the puzzle from Paul Sloane, _Lateral Thinking Puzzlers_. ]

Show solution

In the book "Lateral Thinking Puzzlers" by Paul Sloane I found a
question the answer to which seems incorrect to me.  [...]  The answer
is: She juggled the balls as she went over the bridge.

It seems to me that the weight on the bridge will still be 120 lb (as
the weight exerted by the truck on the platform in the puzzle discussed
some time ago is still 1500 lb, even when the pigeons are flying inside
the truck).  Am I right?

-- Paul Leyderman <pleydrmn@math.ohio-state.edu>

[ Editor: no replies were found in the collected postings. ]

[ Editor: a 1997 variant without juggling, with a lateral answer. ]

Pamela Segal wrote:
>
> Indiana Jones must escape from a band of cannibles.  He has three
> ten-pound bars of gold and he has to make it over a thin, rickety rope
> bridge.  The bridge can hold 170 pounds and Indiana weighs 150.  How
> does he get across with all three diamonds?

I'm going to make a few assumptions (in addition to changing diamonds
to gold)

1) the bridge is made of rope and wood, as in "temple of doom", the
post indicates this with the word rickety (I've not seen a rickety
rope).

2) the entire bridge can support an additional 170 pounds, not each
board as then Indy could simpley step on two boards at once.

3) A normal walking motion will not increase Indy's weight beyond 150
lbs.

4) Indy has at least a 30 second lead on the cannibals, this would be
enough time for him to cross sans bars without a cannibal jumping on
the bridge, which would cause it to fall.

Indy leaves the bars near one side and breaks out every-other board
till ten pounds of wood are gone, he quickly goes back, picks up the
bars and crosses breaking out the boards behind him so that the
cannibals can not follow then walks calmly across.

-- John Loehrlein <jloehr@iastate.edu>, April 1997