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Need help on a Calculus Problem

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Old Nov 17, 2008 | 11:16 AM
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Need help on a Calculus Problem

I'm stumped on this one

An offshore well is located in the ocean at a point W, which is 5 miles from the closest shorepoint A on a straight shoreline. The oil is to be piped to a tank at Shorepoint B, that is 8 miles from A, by piping it on a straigh tline under water from W to some shorepoint P between A and B and hen on to B via a pipe along the shoreline. If the cost of laying pipe in $100,000 per mile under water and $75,000 per mile over land, where should the point P be located to minimize the cost of laying the pipe?
 
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Old Nov 17, 2008 | 12:09 PM
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well its been a while but most places on the shoreline equal or exceed 950,000$, if there is a location that will be less than 950,000 it is between mile 7 to 8 ? For example at 7 miles away from point A on the shore its 8.7 miles aeay from W -cost is 945,000 at 7.5 miles away from A on the shore its 9.1 from W -cost is 947,000. Hope this helps.
 
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Old Nov 17, 2008 | 12:15 PM
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This is a trick question for three reasons:
1. See the "Entitlement" thread in this section. Accordingly, any answer is correct.
2. Eco-***** have stifled any offshore oil drilling, so the problem lacks relevance.
3. Whether you're on land or sea, laying pipe can cost you a lot of money. So be careful
 
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Old Nov 17, 2008 | 12:59 PM
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Six miles away from point A is where the pipeline should hit land, with two miles of onshore pipeline.

To do this you need two equations - one is the formula 100000X+75000Y which you want to minimixe. The other equation is the one for the right triangle with two variable sides. The one side is fixed at 5 miles and the other one ranges from 0 to 8 miles. So, your other equation is X=SQRT(5^2+(8-y)^2). Plug the equation above into the original equation, take the derivative and set it equal to zero and solve for X.

Or you could just do it in a spreadsheet and pick the smallest number like I did....
 
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Old Nov 17, 2008 | 01:09 PM
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6 miles from point A would give you 8 miles of underwater pipe and 2 miles of shoreline pipe = 950,000 the dollar amount as if you went all underwater?
 
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Old Nov 17, 2008 | 02:59 PM
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Originally Posted by SOB Racing
6 miles from point A would give you 8 miles of underwater pipe and 2 miles of shoreline pipe = 950,000 the dollar amount as if you went all underwater?
Not quite. 6 miles from A would be 7.81 miles underwater since it would be the hypotenuse of a right triangle with sides of 5 miles and 6 miles. This would be $781,000 of underwater pipe and $150,000 onshore pipe or $931,000 total.

Going straight from the well to the tank would be the hypotenuse of a right triangle with sides of 8 and 5 miles or 9.43 miles.
 
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Old Nov 17, 2008 | 08:11 PM
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Point P should be in my back yard with a spigot on it.

 
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Old Nov 18, 2008 | 06:30 PM
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Are those really answers or guesses and I concur with ckal704 point p in my backyard as wekk
 
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Old Nov 18, 2008 | 06:37 PM
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oops... well
 
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Old Nov 18, 2008 | 06:59 PM
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Originally Posted by harley scott
Are those really answers or guesses
I believe my answer to be correct.
 
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Old Nov 18, 2008 | 07:06 PM
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I have not checked Nitam's math, but his thought process is correct. you need to come up with asingle formula with 1 variable, take the derivative, set equel to zero, solve for x.
 
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Old Nov 19, 2008 | 05:39 AM
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Originally Posted by Jimmy Dean
I have not checked Nitam's math, but his thought process is correct. you need to come up with asingle formula with 1 variable, take the derivative, set equel to zero, solve for x.
I had a fluid dynamics professor that never checked the math, just looked at how the problem was set up - the numerical answer wasn't important as long as you knew how to get there.

I wish the OP would chime in and let us know how we did.
 
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Old Nov 20, 2008 | 07:45 AM
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I finally sat down and did the problem out and came up with the following solution:

Point P should be 5.7 miles from point A, resulting in 7.58 miles of underwater pipe and 2.3 miles of on land pipe. Total cost comes to $930,722.

But, that is only $18,000 less than running the pipe completely underwater. You'd spend that much and then some operating and maintaining the pump station.

So, like was stated above - trick question.
 
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Old Nov 20, 2008 | 08:49 AM
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Sorry for takin so long to get back, been busy, Nitramjr is correct along with Jimmy Dean. You had to take a triangle, get one variable, take the derivative and set to zero. Thanks to Nitramjr and Jimmy Dean for helpin out
 
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Old Nov 20, 2008 | 09:55 AM
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Sorry....couldn't help it!
 
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