Find radius and height of a cylindrical container with Minimum Cost of Construction

Calculus Tutorial

Find radius and height of a cylindrical container with Minimum Cost of Construction

Intro

This is another hot topic that will absolutely have one or more problems on your calculus exam. For this type of problem first you’ll need an equation of height in terms of radius, so that you can end up with only a variable of r for the equation of minimum cost. Next is to calculate the minimum total cost by adding total cost of bottom, top, and side of the cylindrical container. Finally, differentiate the total cost equation by taking the first derivative of radius r. You will then use the solutions of r to find h and the minimum cost.

Sample Problem

A cylindrical can is to hold 20\pim^3 The material for the top and bottom costs $10/m^2 and material for the side costs $8/m^2 Find the radius r and height h of the most economical can.

Solution

1. Total volume of cylinder: 20\pi = (area of base)*height = ( \pir^2)h, we need to solve h in terms of r, so h = 20/r^2

2. List the minimum equation for total cost of construction of cylinder:
C = (total cost of bottom) + (total cost of top) + (total cost of side)
= (unit cost of bottom)(area of bottom) + (unit cost of top)(area of top) + (unit cost of side)(area of side)
= $10(\pir^2) + $10(\pir^2) + $8(2\pirh) = 20\pir^2 + 16\pirh

3. Substitute h with 20/r^2 in step 1 to cost equ in step 2:
C = 20\pir^2 + 320\pi/r

4. Now differentiate the C equ, we get C’ = 40\pir +320(-1/r^2) = 40\pir[r^2/r^2] – 320\pi/r^2 = 40\pi(r^3-8)/r^2 = 0, so solve for r and we get r = 2. Then h = 20/2^2 = 20/4 = 5

5. Calculate C by plugging r and h values from #4: C = $240\pi = $754(ans)



About The Author

Math And Science Instructor/ Private Tutor
I take every students very seriously. When we first meet, I would like to know about your education background and your own learning methods so I can tell you for any bad learning habits from you. I will also patiently assist you to solve each math and science problem step by step. Regarding ...
Send Email
10 Subjects
KnowRo Tutor
5 Tutorials
$30
San Jose, CA
Learn

Suggested Tutors for Calculus Help

Ad

Varsity Tutors

(855) 475-5132 - Award-Winning Academic & Test Prep Tutors

Ad

Link Educational Institute

Link Educational Institute

Luke N

Bethesda, MD

SAT Instructor And Humanities, Biology

Sophia G

Washington, DC

General Tutor

Leave a Comment

Your email address will not be published. Required fields are marked *

^