Homework Help: math

Posted by Mackenzie on Monday, February 4, 2008 at 8:03pm.

what should be the dimensions of the cylinder if you wanted it to have the least amout of surface area as possible?

the cylinders volume is 100ft cubed

math - bobpursley, Monday, February 4, 2008 at 8:06pm
I assume this is calculus class.

Volume= PI*radius^2*h
h= volume/(PI*radius^2)

Surface=PI*radius^2*2 + PI*radius*height
Surface= PI*radius^2 * 2 + PI*radius*volume/(PI*radius^2)

Take the derivative of surface with respect to radius, set it to zero, and solve for radius.
math - Mackenzie, Monday, February 4, 2008 at 8:08pm
i am only in 7th grade! Could you explain that a little more to me
math - bobpursley, Monday, February 4, 2008 at 8:13pm
Sorry, this question is a typical college level calculus question. For a seventh grader, it is a little harder.

Try this. Graph Surface area vs radius according to the equation I gave you...

Surface= 2*PI*radius^2 + 100/radius
You will see a graph that has a minimum. If you have a graphing calculator, it is easy to graph.

Once you have the minimum, read the radius point on the curve. Then,
Height= 100/(PI*radius^2)

This problem is a bit advanced for a seventh grader.
- math - Mackenzie, Monday, February 4, 2008 at 8:18pm
  i have an answer but i dont know if it is right! will you tell me if i am right or wrong.
  
  i got that the dimensions 31.83098862 ft by 2 ft would have the least surface area for the problem.
  
  am i right or wrong?
  
  can you help me????
math - bobpursley, Monday, February 4, 2008 at 8:27pm
I dont get that. I get the diameter to be 5.84 feet (twice the cube root of 25).
You can figure the height . I get less than four feet.

check me.
- math - Mackenzie, Monday, February 4, 2008 at 8:31pm
  how did you figure that out?
  
  this is what i did!
  
  100 divided by pie and i got 31.83098862 ft and then that multiplied by 2 is 100!
  
  please help me
math - bobpursley, Monday, February 4, 2008 at 8:31pm
One note. I included the ends in the surface area. If they are not to be included, then it is a different answer.
- math - Mackenzie, Monday, February 4, 2008 at 8:33pm
  what ends?
  - math - Mackenzie, Monday, February 4, 2008 at 8:39pm
    please help! explain it to me in a 7th grade way! i am taking pre algebra

Answer this Question

Related Questions

MATH - what should be the dimensions of the cylinder if you wanted it to have ...
Geometry - what are the dimensions of two cylinders where the first cylinder has...
Pre Algabra - If there is a cylinder that has a volume of 100 ft, what would be ...
surface area - Find the surface area of the cylinder in terms of pi. I know the ...
Math: Geometry - The circumference of the base of a cylinder is 16 cm. The ...
Math - Optimization Problem A right circular cylindrical can of volume 128t&...
Physics - Two conducting thin hollow cylinders are co-aligned. The inner ...
Geometry - Two cylinders have the same volume. If the radius of cylinder I is 3 ...
physics - Two conducting thin hollow cylinders are co-aligned. The inner ...
physics - If the aim is to let a 700 kg pump float on the surface of water, how...

For Further Reading

First Name:
School Subject:
Answer: