Imagine two high-voltage-masts/poles

[DaveC426913]

the cable will be hanging down in the shape of a parabola...right??

if yes, then you get a really bad equation in natural logs and roots and stuff. but...it can be solved to get the the distance.

This reminds me of a story about mathematicians who used to use slide rules for EVERYTHING. When asked for the square root of 100, they would race through their calculations to get an answer of 9.9999.. "Sorry, how many decimal places did you want?"

geniusprahar_21: that's a huge hint. Yeeeees, it *would* hang in a parabola, and yeeees, that *would* be hard to calculate...

But before you give up, try drawing the diagram. Accurately.

 

[Jimmy Snyder]

.Yeeeees, it *would* hang in a parabola

No it would not. Please read post #28 of this thread.

 

[Galileo]

It's unbelievable how long this thread lingers and is still receiving clueless answers. The answer has appeared in the thread almost a dozen times for those who took the effort to read.

 

[DaveC426913]

Yeeeees, it *would* hang in a parabola

No it would not. Please read post #28 of this thread.

You misunderstand my post. (And you are, at least technically, incorrect, though you are correct in spirit).

The poster is correct in principle that it forms a parabola (which, technically, it does). It's just a parabola with some very unique values (Google "degenerate parabola") and I expect that if he did the calculations the hard way, he would still arrive at the correct answer - and then slap himself on the forehead.

I'm trying to hint to him that *knowing* it is a parabola is not going to get him to the *easy* answer.

 

[DaveC426913]

It's unbelievable how long this thread lingers and is still receiving clueless answers. The answer has appeared in the thread almost a dozen times for those who took the effort to read.

Some people are still trying to solve it without peeking. Surely you don't object?

 

[Cybersteve]

You misunderstand my post. (And you are, at least technically, incorrect, though you are correct in spirit).
The poster is correct in principle that it forms a parabola (which, technically, it does). It's just a parabola with some very unique values (Google "degenerate parabola") and I expect that if he did the calculations the hard way, he would still arrive at the correct answer - and then slap himself on the forehead.
I'm trying to hint to him that *knowing* it is a parabola is not going to get him to the *easy* answer.

I'm slightly confused - nothing new there!
I think I am the "poster" you're referring to, I did get the answer almost straight away -at least as soon as I tried to draw the situation.
But the link you posted says:
"In 1669, Jungius disproved Galileo's claim that the curve of a chain hanging under gravity would be a parabola"
Now you say it is a parabola, or at least a special kind of parabola.
So who's right? You, me, Galileo or Jungius (whoever he might be)
Lastly don't you think it's about time somebody "put some ink in their pen" and writes the answer in a readable form?

 

[Jimmy Snyder]

Lastly don't you think it's about time somebody "put some ink in their pen" and writes the answer in a readable form?

To read the unreadable answers, drag your mouse across them. They will become readable.

The facts are these. The solution to the immediate problem involves a certain unusual kind of parabola. However, some have opined that in general (not limited to this problem) a hanging cable takes the shape of a parabola. While it is true in this particular case (in a funny way) it is not true in general. In the general case the cable takes the shape of a catenary.

 

[Cybersteve]

Hi jimmysnyder,
I'm not sure who's addressing who(m) anymore.

I knew how to highlight the answers given. I was just surprised that after it had been posted so many times there were still people who haven't seem to have got it yet.

As a newbie here I didn't think it was my place to put them out of their misery and wondered why someone hadn't done so.

 

[Jimmy Snyder]

Hi jimmysnyder,
I'm not sure who's addressing who(m) anymore.

Oops. I'm not making thing clearer am I? That part of my post is in error and I am going over there to edit it right now.

 

[croxbearer]

isn't it that if your draw it in a diagram, it would look like a straight line?

 

[Jimmy Snyder]

isn't it that if your draw it in a diagram, it would look like a straight line?

Response in white Yes, look like one and even more in the mathematical world of puzzles, be one. And as DaveC426913 pointed out, a straight line is a degenerate parabola.

 

[DaveC426913]

a hanging cable takes the shape of a parabola. While it is true in this particular case (in a funny way) it is not true in general. In the general case the cable takes the shape of a catenary.

I stand corrected.

 

[Integral]

This reminds me of a story about mathematicians who used to use slide rules for EVERYTHING. When asked for the square root of 100, they would race through their calculations to get an answer of 9.9999.. "Sorry, how many decimal places did you want?"

Trouble is, in the section of the slide rule that you would be looking at for 9.99 or .999 all you can get is 3 sig digits. It was not till calculators came along that you saw anybody writing down .9999999 and pretending like the last 4 9s had any meaning. Slide rules FORCED you to use only significant digits.

Any way any decent slide rule would give \sqrt 100 = 10 without any round off error, again that is an artifact of calculators.

Yes, I learned to run a slide rule in high school, long before anyone had ever heard of a hand held calculator.

 

[beanybag]

im going to clarify for soem ppl who are waaaaay overdoing this. the poles are 25m high. the cable is 18 m long. when its hanging, it goes 9m down from one pole, then 9m up to connect to the top of the other, so that its hanging at its lowest part 16m off the ground. therefore the poles are no disntance apart. or you could say their distance apart is equal to the widdth of t he cable about. jeez.

 

[Cybersteve]

im going to clarify for soem ppl who are waaaaay overdoing this. the poles are 25m high. the cable is 18 m long. when its hanging, it goes 9m down from one pole, then 9m up to connect to the top of the other, so that its hanging at its lowest part 16m off the ground. therefore the poles are no disntance apart. or you could say their distance apart is equal to the widdth of t he cable about. jeez.

I think you should have stopped before this part -"or you could say their distance apart is equal to the width of the cable about."
You may just have opened up a whole new can of worms!

 

[Nathaniel]

I just got decipher the problem with the help of my pop.

Actually the problem was quite tricky... I have been to a lot of equations using my little knowledge in trigonometry and Geometry...dut it resulted nothing unlike i realized that i needs no trigonometry or Geometry. Here is my answer:

Actually the two poles were not apart they were close together. The distance between poles is 0 meters.

Please tell If I'm right...Thanks.