Search All of the Math Forum:

Views expressed in these public forums are not endorsed by NCTM or The Math Forum.

Notice: We are no longer accepting new posts, but the forums will continue to be readable.

Topic: Cable around the Equator
Replies: 10   Last Post: Jun 17, 2012 2:29 PM

 Messages: [ Previous | Next ]
 Juan Miguel Vilar Posts: 15 Registered: 12/6/04
Re: Cable around the Equator
Posted: Nov 5, 1996 4:08 PM

Not only was his math impeccable, it was also correct! I think that
it passes correctly the sanity check, where is the problem?

Juan Miguel Vilar

On 5 Nov 1996, mfr1 wrote:

> How can adding 50' of slack to the cable spread evenly around the equator
> pass the sanity check! This is why we must not blindly accept mathematical
> results. That is the lesson to be learned from this geometry problem.
>
> lipp@educ.umass.edu wrote in article
> <Pine.PMDF.3.91.961104130200.557939369A-100000@oitvms.oit.umass.edu>...

> >
> >
> > On Mon, 4 Nov 1996, mfr1 wrote:
> >

> > > Ma Bell wants to place a telephone cable around the equator. She adds
> 50
> > > feet to the length of the cable beyond what is required. This slack in
> the
> > > cable allows the cable to be strung up above the ground. How high up
> from
> > > the surface of the earth will the cable stand? You can assume that the
> > > earth is a perfect sphere.
> > >
> > > In your mind, run a sanity check on your answer to see if it makes

> sense.
> > >
> > Surprisingly, you will be able to walk under the cble easilty. Since the
>
> > circumference of a circle is C = 2piR, each increase in R obf 1 foot
> > increases the circumference by 2pi feet. since the cable has been
> > increased by 50 feet the radius of the cable-circle will be increased by
> > 50/2pi or about 8 feet!
> >
> > Alan Lipp
> >

>

Date Subject Author