My Math Forum  

Go Back   My Math Forum > High School Math Forum > Trigonometry

Trigonometry Trigonometry Math Forum

LinkBack Thread Tools Display Modes
June 25th, 2015, 12:38 PM   #1
Joined: Jun 2015
From: Chicago

Posts: 2
Thanks: 0

Circumference of part of a circle

Hi Guys

Hope this is in correct forum.

I have a roll of paper whose diameter is 50-inches and it weighs 4,000lbs (width is about 75-inches if it matters).

These are the only attributes I know.

I'm trying to figure out what the diameter would be if I used 3,000lbs (i.e. I've used 75% of the weight). It's wound on a core whose external diameter is about 6-inches (but I can ignore this if needed for simplicity).

I'm figuring there has to be a way to figure out the diameter remaining if the 75% is left, but I'm drawing a blank. (I added a diagram in the attached)

Can someone point me in right direction?


Attached Images
File Type: jpg AreaOfCircle.jpg (8.8 KB, 3 views)
SlipperyEel is offline  
June 25th, 2015, 01:00 PM   #2
Global Moderator
Joined: May 2007

Posts: 6,704
Thanks: 669

Weight is proportional to volume. Volume of cylinder is proportional to $\displaystyle r^2$.

Roll of paper volume proportional to $\displaystyle 50^2-6^2=2464$.

Reduce volume proportional to .75x2464=1848.

Final diameter = $\displaystyle \sqrt{1848+36}=43.4$.
mathman is offline  
June 26th, 2015, 03:44 AM   #3
Joined: Jun 2015
From: Chicago

Posts: 2
Thanks: 0

Thanks a lot Mathman!
SlipperyEel is offline  

  My Math Forum > High School Math Forum > Trigonometry

circle, circumference, part

Thread Tools
Display Modes

Similar Threads
Thread Thread Starter Forum Replies Last Post
circumference of a circle fil1977 Calculus 4 April 18th, 2015 06:24 AM
Circumference of a circle Chikis Elementary Math 7 January 22nd, 2014 04:46 PM
Why is area of circle exactly divisible by circumference? BenFRayfield Algebra 4 November 22nd, 2013 10:50 PM
Change in X Y along circle's circumference jimmyfo Algebra 8 May 15th, 2009 09:40 AM
circumference of a circle as a function of area empiricus Calculus 3 December 31st, 1969 04:00 PM

Copyright © 2019 My Math Forum. All rights reserved.