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Sunday, November 7, 2010
Ch 11_1 #1
Use mass density formula to calculate unknown quantity
7 comments:
Anonymous
said...
I've converted everything (mass and volume) to SI units, and I've tried doing the total mass of the system divided by the total volume of the system. It told me that was wrong. So now I've tried the average mass of the system divided by the average volume, and the mass of each divided by the total volume and averaged those, and none of these are correct! What am I doing wrong??? Please help!
I did the total mass divided by total volume, and got close to the answer but had to try a few different numbers in the tens place to round it right (I think because their value for the density of gasoline was different than the one I used). I got 860 kg/m3 and had to move it down to 840 kg/m3 before it would accept it (the actual answer was 820 for mine).
The book by Knight et all (recommended for the class) in front of the help room has a table with densities of liquids. It lists gasoline density as 680 kg/m^3. You may want to use this number as your input.
I still don't understand how to do this. For part b I added the two volumes after converting both to kg and divided that into the two masses I came up with after multiplying the densities with given volumes. My answer was way too high than the accepted value which I guessed to be close to the first answer. I was also using 10^3=10,000 for density of water.
7 comments:
I've converted everything (mass and volume) to SI units, and I've tried doing the total mass of the system divided by the total volume of the system. It told me that was wrong. So now I've tried the average mass of the system divided by the average volume, and the mass of each divided by the total volume and averaged those, and none of these are correct! What am I doing wrong??? Please help!
I did the total mass divided by total volume, and got close to the answer but had to try a few different numbers in the tens place to round it right (I think because their value for the density of gasoline was different than the one I used). I got 860 kg/m3 and had to move it down to 840 kg/m3 before it would accept it (the actual answer was 820 for mine).
The book by Knight et all (recommended for the class) in front of the help room has a table with densities of liquids. It lists gasoline density as 680 kg/m^3. You may want to use this number as your input.
where is the equation for the pavg?
You have to derive it yourself.
Look at the expression for rho and think what enters for mass and volume in case you add those 2 liquids together.
I still don't understand how to do this. For part b I added the two volumes after converting both to kg and divided that into the two masses I came up with after multiplying the densities with given volumes. My answer was way too high than the accepted value which I guessed to be close to the first answer. I was also using 10^3=10,000 for density of water.
10^3=1000 perhaps that was a problem
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