A 30-gallon tank initially contains 15 gallons of salt water containing 3 pounds of salt. Suppose salt water containing 1 pound of salt per gallon is pumped into the top of the tank at the rate of 2 gallons per minute, while a well-mixed solution leaves the bottom of the tank at a rate of 1 gallon per minute. How much salt is in the tank when the tank is full?

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
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A 30-gallon tank initially contains 15 gallons of salt water containing 3 pounds of salt. Suppose salt water
containing 1 pound of salt per gallon is pumped into the top of the tank at the rate of 2 gallons per minute,
while a well-mixed solution leaves the bottom of the tank at a rate of 1 gallon per minute. How much salt
is in the tank when the tank is full?
Transcribed Image Text:A 30-gallon tank initially contains 15 gallons of salt water containing 3 pounds of salt. Suppose salt water containing 1 pound of salt per gallon is pumped into the top of the tank at the rate of 2 gallons per minute, while a well-mixed solution leaves the bottom of the tank at a rate of 1 gallon per minute. How much salt is in the tank when the tank is full?
Expert Solution
Step 1

Given that

dN(t)dt = flux of salt in - flux of salt out

The salt flux into the tank is always C_in * f_in, where C_in is the concentration of salt in the stream entering the tank, and f_in is the solution's flow rate. In this case:

The flux of salt in 

= 1 lb/gal * 2 gal/min = 2 lb/min.

The flux of salt out of the tank is given by

C(t)*fout=N(t)*foutV(t)

Where C(t) = N(t)/V(t) is the concentration of salt in the tank at time t.

V(t) is the volume of solution in the tank, and f_out is the flow rate of solution exiting the tank.

 

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