MHB Cat's question at Yahoo Answers regarding approximate integration

MarkFL
Gold Member
MHB
Messages
13,284
Reaction score
12
Here is the question:

Calculus question: which would best approximate total water consumption of storage tank?


Water is pumped from a storage tank and the flower of water from the tank is given by C(t) = 25e ^-0.05(t-15)^2 thousand gallons per hour, where t is the number of hours since midnight. Which of the following best approximates the total water consumption for one day (in thousands of gallons)?

a) 33.964
b) 164.202
c) 197.727
d) 198.166
e) 202.144

How do you find this answer? Please explain how you work through this problem, thank you!

I have posted a link there to this thread so the OP can view my work.
 
Mathematics news on Phys.org
Hello Cat,

To find the total consumption $T$ of water for 24 hours, we may state:

$$T=\int_{0}^{24} C(t)\,dt=25\int_{0}^{24} e^{-\frac{(t-15)^2}{20}}\,dt$$

Now, the integrand in this problem does not have an anti-derivative expressible in elementary terms, so we must use either the error function or approximate integration. For simplicity of computation and aided by a computer, let's use the Midpoint Rule and state:

$$T\approx\Delta t\sum_{k=0}^{n-1}\left(C\left(\frac{t_{k}+t_{k+1}}{2} \right) \right)$$

Now, we find that:

$$\Delta t=\frac{24}{n}$$

$$t_k=\frac{24k}{n}$$

$$\frac{t_{k}+t_{k+1}}{2}=\frac{12}{n}(2k+1)$$

Hence:

$$T\approx T_n=\frac{600}{n} \sum_{k=0}^{n-1}\left(\exp\left(-\frac{\left(\dfrac{12}{n}(2k+1)-15 \right)^2}{20} \right) \right)$$

Now, at the site Wolfram|Alpha: Computational Knowledge Engine I used the command:

sum of (600/n)exp(-((12/n)(2k+1)-15)^2/20) for k=0 to n-1

where I substituted powers of 10 for $n$ and obtained (to 3 decimal places):

[TABLE="class: grid, width: 200"]
[TR]
[TD]$n$[/TD]
[TD]$T_n$[/TD]
[/TR]
[TR]
[TD]10[/TD]
[TD]197.814[/TD]
[/TR]
[TR]
[TD]100[/TD]
[TD]197.729[/TD]
[/TR]
[TR]
[TD]1000[/TD]
[TD]197.728[/TD]
[/TR]
[TR]
[TD]10000[/TD]
[TD]197.728[/TD]
[/TR]
[/TABLE]

Thus, the choice given by c) is the closest.
 
Insights auto threads is broken atm, so I'm manually creating these for new Insight articles. In Dirac’s Principles of Quantum Mechanics published in 1930 he introduced a “convenient notation” he referred to as a “delta function” which he treated as a continuum analog to the discrete Kronecker delta. The Kronecker delta is simply the indexed components of the identity operator in matrix algebra Source: https://www.physicsforums.com/insights/what-exactly-is-diracs-delta-function/ by...
Fermat's Last Theorem has long been one of the most famous mathematical problems, and is now one of the most famous theorems. It simply states that the equation $$ a^n+b^n=c^n $$ has no solutions with positive integers if ##n>2.## It was named after Pierre de Fermat (1607-1665). The problem itself stems from the book Arithmetica by Diophantus of Alexandria. It gained popularity because Fermat noted in his copy "Cubum autem in duos cubos, aut quadratoquadratum in duos quadratoquadratos, et...
I'm interested to know whether the equation $$1 = 2 - \frac{1}{2 - \frac{1}{2 - \cdots}}$$ is true or not. It can be shown easily that if the continued fraction converges, it cannot converge to anything else than 1. It seems that if the continued fraction converges, the convergence is very slow. The apparent slowness of the convergence makes it difficult to estimate the presence of true convergence numerically. At the moment I don't know whether this converges or not.
Back
Top