# Module

• May 15th 2013, 07:55 PM
pczort
Module
does anyone understand these.

1. Two roads intersect at right angles. A water spring is located 60 m from one road and 50 m from the other road. A straight path is to be laid out to pass the spring from one road to the other. Find the least area that can be bounded by the roads and the path.

2.
A commercial packing company wishes to build a shipping box. The box is to be made from a rectangular piece of cardboard 10 m long and 5 m wide by cutting equal squares from each corner and then folding up the remaining sides. What is the maximum volume that the box can have?

3.
A rectangular piece of metal is 33.0 cm long and 26.4 cm wide. A rectangular box is to be formed by cutting a square out of each corner and turning up the remaining sides. The box does not have a top. Determine the size of the square that should be cut out so that the box has a maximum volume.

4.
A pig farmer wishes to fence his rectangular field so that it will contain an area of 167 square meters. If the cost is 2 dollars per meter along two sides and one end and 4 dollars per meter along the other end, calculate the dimensions which give the least cost for the fence.

5.
A farmer plans to build a storage bin. This bin is to be an open-top rectangular tank with square base and is to have a volume of 12 cubic meters. The cost of the bottom is \$17 per square meter and the cost of the sides \$2 per square meter. Find the most economical dimensions for the tank.

6.
The voltage in a circuit is given by the formula V = 13t3 - 57t. Find the values for t for which V is a maximum or a minimum.

7. The power delivered to a circuit by a 15 volt generator of internal resistance 2 ohms when the current is i amperes, is 15i - 2i2 watts. For what current will the generator provide maximum power?
• May 15th 2013, 08:53 PM
ibdutt
Re: Module
You must show us as to what effort you have made and where you got stuck. that is the only way to understand the subject. Anyhow I have given some lead for the first one. Show your effort on the other questions.Attachment 28383
• May 16th 2013, 07:13 AM
hollywood
Re: Module
In each case you have a function that needs to be minimized. The functions seem to be pretty easy to determine - area of a triangle, perimeter of a square, etc. In later problems, they are actually given.

To find the minimum or maximum, set the derivative to zero and solve.

I don't think it happens on these problems, but the minimum or maximum can also occur when the derivative doesn't exist or at the endpoints. So you need to check all three cases.

- Hollywood
• May 16th 2013, 07:19 PM
ibdutt
Re: Module
In fact i would differ a bit, in that we cannot consider a maxima or minima at the end points. it is because of the definition of these points. For example local maxima is the value of the function which is maximum in the neighborhood of that point etc.
• May 16th 2013, 09:11 PM
hollywood
Re: Module
I must not understand what you're saying. For the function f(x)=2x on [0,1], the minimum and maximum are both at endpoints.

- Hollywood
• May 16th 2013, 10:15 PM
MINOANMAN
Re: Module
I believe you have both misundestood the local max/min of a function with the absolute max or min of a continuous function in an interval [a,b]
Anyway the answer to the first is 1350 sq metres.
• May 16th 2013, 10:50 PM
ibdutt
Re: Module
there is no confusion what so ever: the local maxima / minima cannot be at the end points where as absolute maximum / minimum can be at the end points
• May 16th 2013, 11:14 PM
MINOANMAN
Re: Module
Quote:

Originally Posted by ibdutt
there is no confusion what so ever: the local maxima / minima cannot be at the end points where as absolute maximum / minimum can be at the end points

I agree...............
• May 21st 2013, 07:36 PM
pczort
Re: Module
i got 6000 for number 1