(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Given a pipe with 8cm circumference and length 20cm that is 8 turns of wire wrapped around a pipe, what's the length of the wire?

2. Relevant equations

circumference=2(pi)r=diameter*pi (I think)

3. The attempt at a solution

This is pic with problem. My approach, first, take circumference of 8cm. set to formula to find radius, which can then be used to find diameter.

8cm=2(pi)r..r=4cm/pi

Then pic shows the tube being "divided" into 8 pieces. I then draw a diagram, and measure length as the sum of the diagonal blue parts + the sum of the nonvisible imaginary lines passing behind the tube as it revolves. Tricky because there are 8 diagonal lines and 7 horizontal lines... o.o

So yeah, r=4cm/pi, so d=8cm/pi or 2.55. This is the horizontal part. For the vertical part of the diagram (if you cut the tube into eight thingies), I took the height of 20cm, divided by 8 (you see 8 sections on the pic), and got 2.5. Using pythagorean theorem to find the diagonal, 2.5 squared plus 2.55 squared is 12.7525, so diagonal is 3.57.

Now I have diagonal, add the 8 diagonal parts together, so 8(3.57)=28.56. +7(2.55)=46.41.

But then.. The horizonal part, instead of a straight edged distanced, could also be half of the circumference, or pi*r.. But then that diagonal across the tube isn't flat edged either.. oii

The answer is 67.05 for those that can get it right.

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# Homework Help: Wire wrapped around a pipe

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