Differential Equations Compartmental Analysis Word Problem

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SUMMARY

The discussion focuses on a differential equations word problem involving two 60-gallon tanks. Fresh water is pumped into the first tank at a rate of 3 gallons per minute, diluting the brine initially present. The problem requires determining when the water in the second tank, which starts with pure water, will be the saltiest and the concentration of salt at that time. The established answers are that the water in the second tank will taste saltiest at 20 minutes, with a salt concentration of 1/e compared to the original brine.

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  • Understanding of differential equations, specifically first-order linear equations.
  • Familiarity with compartmental analysis in fluid dynamics.
  • Knowledge of concepts related to mixing and concentration changes over time.
  • Ability to interpret and solve word problems involving rates and concentrations.
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  • Study the application of first-order differential equations in real-world scenarios.
  • Explore compartmental modeling techniques in systems of differential equations.
  • Learn about the method of integrating factors for solving linear differential equations.
  • Investigate the concept of perfect mixing and its implications in fluid dynamics.
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Hello, I am trying to tackle a word problem in differential equations, but the setup has flummoxed me. Thank you in advance to any advice/help given.

Homework Statement



Beginning at time t  0, fresh water is pumped at
the rate of 3 gal/min into a 60-gal tank initially filled
with brine. The resulting less-and-less salty mixture
overflows at the same rate into a second 60-gal tank
that initially contained only pure water, and from
there it eventually spills onto the ground. Assuming
perfect mixing in both tanks, when will the water in
the second tank taste saltiest? And exactly how salty
will it then be, compared with the original brine?


Homework Equations


ds/dt = input - output

du/dt = previous output - output


The Attempt at a Solution


I have included a picture of a scratch piece of paper I am working on to demonstrate my work.
 

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I should have mentioned that the stated answer is 20 minutes, for part one, and 1/e for part 2.
 
Question: A clock's minute hand has length 4 and its hour hand has length 3. What is the distance between the tips at the moment when it is increasing most rapidly?(Putnam Exam Question) Answer: Making assumption that both the hands moves at constant angular velocities, the answer is ## \sqrt{7} .## But don't you think this assumption is somewhat doubtful and wrong?

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