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# percentage uncertaties help! watch

1. Calculate the relative uncertainty, in percent, of:
The density of a cuboid block of iron whose lengths are known to 2% and whose mass is known to 0.1%. (Equation: density=massvolume)

Can someone help me with this question please, I've been stuck on it for so long, I don't get it.
2. I might be wrong, but I think this is just a simple sum, the answer being you have to add up the percentage uncertainties. When you are multiplying/diving two values with known %uncertainty, you just add both of the %uncertainties together. Volume of a cuboid is l x l x l so the %uncertainties of length would add up, equallling 2%+2%+2% = 6%
Density = mass x volume so the %uncertainty is 0.1%+6% = 6.1%

http://www.thestudentroom.co.uk/show....php?t=2661762
http://www.thestudentroom.co.uk/show....php?t=2622706
3. (Original post by azefayuu)
I might be wrong, but I think this is just a simple sum, the answer being you have to add up the percentage uncertainties. When you are multiplying/diving two values with known %uncertainty, you just add both of the %uncertainties together. Volume of a cuboid is l x l x l so the %uncertainties of length would add up, equallling 2%+2%+2% = 6%
Density = mass x volume so the %uncertainty is 0.1%+6% = 6.1%

http://www.thestudentroom.co.uk/show....php?t=2661762
http://www.thestudentroom.co.uk/show....php?t=2622706
Yes, you simply add the percentage uncertainties.

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