Homework Help: Percent Uncertainty

1. Aug 16, 2010

iRaid

I have 2 problems that I'm wondering if they're right or not... Thanks for the help.

1. The problem statement, all variables and given/known data
10) What is the area, and its approximate uncertainty, of a circle of radius 3.8 x 104cm?

2. Relevant equations
A=πr2

3. The attempt at a solution
A=π380002
A=4536459792cm2
Then, I did the same thing with 37999 (the uncertainty is $$\pm$$ 1) to find the difference in the area to be 238758.
$$238758/4536459792$$ x 100% = .0053% uncertainty.

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1. The problem statement, all variables and given/known data
11) What, roughly, is the percent uncertainty in the volume of a spherical beach ball whose radius is r=2.86$$\pm$$0.09m?

2. Relevant equations
A=$$4/3$$πr3

3. The attempt at a solution
A=$$4/3$$π2.863
A=97.99m3
I then did the same thing with 2.77 to get that area to be 89.03m3.
97.99-89.03=8.96
$$8.96/97.99$$x100%=9% uncertainty.