Flag Pole

Flag Pole

Posers and Puzzles

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Standard membertalzamir
Art, not a Toil

60.13N / 25.01E

Joined
19 Sep 11
Moves
56993
24 Oct 11

A flagpole has diameter of 10 centimeters (4"😉. A rope that is 10 meters (30'😉 long has been attached to the top. It spirals around the flagpole 25 times before the other end of the rope reaches the ground. How tall is the flag pole?

f
Standard memberforkedknight
Defend the Universe

127.0.0.1

Joined
18 Dec 03
Moves
16687
24 Oct 11
1 edit

I get

25 * sqrt(40^2 - 10pi^2) = ~619cm

Standard membertalzamir
Art, not a Toil

60.13N / 25.01E

Joined
19 Sep 11
Moves
56993
24 Oct 11

I wonder why the answer I got is exactly 25 times yours..? And that does make the respectable-sized flagpole I had in mind..?

m
Standard membermtthw

Joined
07 Sep 05
Moves
35068
24 Oct 11
1 edit

I agree with forkedknight's answer:

sqrt[L^2 - (25*pi*d)^2]
,
where L = length of rope and d = diameter.

f
Standard memberforkedknight
Defend the Universe

127.0.0.1

Joined
18 Dec 03
Moves
16687
24 Oct 11
2 edits

Originally posted by talzamir
I wonder why the answer I got is exactly 25 times yours..? And that does make the respectable-sized flagpole I had in mind..?
25 times what i got is 15x longer than your rope...

*edit* I see your response was before I did my edit, and my edit added the multiplier of 25 that i missed in my initial calculation (I broke the flag pole up into 25 rectangles across which the rope makes the hypotenuse)

Standard membertalzamir
Art, not a Toil

60.13N / 25.01E

Joined
19 Sep 11
Moves
56993
24 Oct 11

So we both multiplied by 25? That makes a very awesome flagpole. ^_^ So yes, a bit over six meters it is.