D.E. Problem Explained: Limits and Units

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SUMMARY

The discussion centers on a differential equation problem concerning the rate of change of water level in a tank. The correct formulation of the equation is dh/dt = 1/100 - (1/4)h, where water enters at a rate of 1 cubic foot per second and exits at a rate proportional to the height of the water. The confusion arose from misinterpreting the term "1/4h" as "1/(4h)", leading to incorrect conclusions about the limits of the water level. The proper understanding of units and the relationship between inflow and outflow is crucial for solving this problem accurately.

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[SOLVED] D.E. problem

Homework Statement


See the attachment.

Homework Equations


The Attempt at a Solution


dh/dt = 1/100 - 1/4h

Why is the limit not h = 1/25 or 4 cubic feet?
 

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Please be careful about parentheses! I had first interpreted "1/4h" as "1/(4h)" and got a silly answer!

However, your equation is wrong. Since water comes in at 1 cubic foot per second and the "water tower" has a uniform cross section area of 100 square feet, yes, that causes the water level to rise at 1/100 feet per second which are the correct units for dh/dt.

But the water is also going out at (1/4)t cubic feet per second which is NOT the correct units. If water is going out at (1/4)t cubic feet per second, how fast is the water level dropping in feet per second?
 

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