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DE: Unit Cancellations Not Making sense

by dillonmhudson
Tags: cancellations, sense, unit
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dillonmhudson
#1
Jan30-11, 08:02 PM
P: 50
1. The problem statement, all variables and given/known data
Consider a tank used in certain hydrodynamic experiments. After one experiment the tank contains 200 liters of a dye solution with a concentration of 1 g/liter. To prepare for the next experiment, the tank is to be rinsed with fresh water flowing in at a rate of 2 liters/min, the well-stirred solution flowing out at the same rate. Find the time that will elapse before the concentration of dye in the tank reaches 1% of its original value.

2. Relevant equations
[tex]\frac{dQ}{dt}[/tex]=rate in - rate out

3. The attempt at a solution
Why the heck do they cancel units incorrectly?
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Dick
#2
Jan30-11, 08:28 PM
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Hard to say until you tell us what the heck Q is.
dillonmhudson
#3
Jan30-11, 08:30 PM
P: 50
Q is the amount of dye in the tank.
dQ is the rate of change of the amount of dye in the tank.

Dick
#4
Jan30-11, 08:37 PM
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DE: Unit Cancellations Not Making sense

Quote Quote by dillonmhudson View Post
Q is the amount of dye in the tank.
dQ is the rate of change of the amount of dye in the tank.
Then all the terms in your equation should have units of grams of dye per minute. I think the Q/100 l/min should be g/min. Probably a typo.
dillonmhudson
#5
Jan30-11, 08:39 PM
P: 50
Ok that's what I was hoping - thank you.


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