Re: Aaahhh... I can't believe this

In article
<Tt2dnQMObbEzB2DYnZ2dnUVZ_vGinZ2d@xxxxxxxxxxx>,
Mark Nudelman <markn@xxxxxxxxxxxxxxxxxxxxx> wrote:

On 3/18/2007 1:59 AM, alertjean@xxxxxxxxxxxxxx wrote:
Well,
The situation is a case in which you tie a rope around earth's equator
(around 40,000 km) and you increase the length of the rope by one
metre. How much should you increase the radius of earth so that the
new loop fits perfectly (slack=0). Guess how much ? Dont calculate !
Answer is sixteen centimetres(1/2pi).
and the important thing is that the answer is always 16 cm even when
the body under consideration is Sun,moon or a bicycle tyre.

2.pi.R=C
2.pi.(R+dR)=(C+dC)
dR=dC/2.pi

Anyone has more of such difficult to believe questions ?
Lets share
Jean

Two metal rails, each one mile long, are laid end-to-end making a 2-mile
long rail. The free end of each rail is staked to the ground, but the
joint where the rails *** against each other is free to move. Each
rail expands by one inch due to thermal expansion, but remains straight
and in contact with the other rail, thus causing the joint to rise above
the ground. How high does the joint rise?

The more interesting portion of this question is to
calculate the answer without the substantial loss of
significant figures one suffers with the naive calculation.
--
Michael Press
.

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