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I was wondering how do you calcultate physics problems when you must also note the error of measurement.

I mean if you have a weight-scale that has a percison of 20 g, and lets say that the scale shows 0,7 kg. Does that mean you have 0,7 kg +- 0,02 kg or 0,7 +- 0,01 kg. Or what. And if you have in a test. Something like this

mass of object is 20(1 +- 0,05)g what does that mean? Or if you need to calculate the speed of a bullet from kinetical energy. Let say the data is weigh 6,00 g and Wk = 3,12 J. The first data is of 2 or 3? significant figure the other is of 3 significant numbers. What is the precision of the resoult. You have v = sqrt((2*Wk)/m)) = 1,01980 do you write 1,019 or 1,02 +- xx? I am a bit puzzled by this +- precision and uncertanty. Can somebody explain this to me in simple language or give a link to a web site. I tried to ask my physics profesor but he just said "Look it up". I looked at the NIST referance for Constants, Units and Uncertanty but that make me more puzzled than before.

Thanks

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# Homework Help: Precision in Physics problems

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