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# uncertainties as physics Watch

1. a student wishes to determine the density of lead. she measures the mass and diameter of a small sphere of lead

mass = (o.506 +- 0.005)g
diameter = (2.20 +- 0.02)mm

what is the best estimate of % uncertainty in her value of density
2. (Original post by uzer)
a student wishes to determine the density of lead. she measures the mass and diameter of a small sphere of lead

mass = (o.506 +- 0.005)g
diameter = (2.20 +- 0.02)mm

what is the best estimate of % uncertainty in her value of density
Moved to the physics section for you

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3. (Original post by uzer)
a student wishes to determine the density of lead. she measures the mass and diameter of a small sphere of lead

mass = (o.506 +- 0.005)g
diameter = (2.20 +- 0.02)mm

what is the best estimate of % uncertainty in her value of density
I get a bit confused with this, but I think this is what you want to do:
1) Work out the %uncertainty in each measurement

EDIT: woops, thought you had volume, not diameter. In which case you need the %uncertainty in volume, so I think that's just 3X the uncertainty in the diameter. Will actually go off and learn this.
4. (Original post by uzer)
a student wishes to determine the density of lead. she measures the mass and diameter of a small sphere of lead

mass = (o.506 +- 0.005)g
diameter = (2.20 +- 0.02)mm

what is the best estimate of % uncertainty in her value of density
http://www.thestudentroom.co.uk/show...ht=uncertainty

Contains all relevant information in the OP.
5. (Original post by uzer)
a student wishes to determine the density of lead. she measures the mass and diameter of a small sphere of lead

mass = (o.506 +- 0.005)g
diameter = (2.20 +- 0.02)mm

what is the best estimate of % uncertainty in her value of density
Yes, as the poster above suggests, take a look at the "sticky" thread (Combining uncertainties) at the top of this forum, which describes how to do this.
If there is then anything you don't understand in that post, come back here and ask.
6. (Original post by Stonebridge)
Yes, as the poster above suggests, take a look at the "sticky" thread (Combining uncertainties) at the top of this forum, which describes how to do this.
If there is then anything you don't understand in that post, come back here and ask.
i still dont know how to obtain the uncertainty for the volume
7. (Original post by uzer)
i still dont know how to obtain the uncertainty for the volume
What is the % uncertainty in the diameter?
What is the formula for volume using diameter?
8. (Original post by Stonebridge)
What is the % uncertainty in the diameter?
What is the formula for volume using diameter?
i honestly dont have a clue
9. (Original post by uzer)
i honestly dont have a clue

I thought you had worked out the % uncertainty in the mass. So why can't you do the same for the diameter?

Mass:
mass = (0.506 +- 0.005)g
What is 0.005 as a % of 0.506?

Diameter:
diameter = (2.20 +- 0.02)mm
What is 0.02 as a % of 2.20?

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