(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

[tex]V=\pi r^{2} h[/tex]

The uncertainties in V and h are shown below

V 7%

h 3%

The approximate uncertainty in r is:

A. 10% B. 5% C. 4% D. 2%

2. The attempt at a solution

According to the key the correct answer is B. This answer can be calculated by:

[tex]r^{2}=\frac{V}{\pi h}[/tex]

which gives 3%+7% = 10% uncertainty

and subsequently

[tex]r=\sqrt{\frac{V}{\pi h}}[/tex]

giving 10% * 1/2 = 5%

However:

if the value of 5% uncertainty for r is inserted in the original equation it all doesn't make sense:

[tex]V=\pi r^{2} h[/tex] should then give an uncertainty for V of 3%+5%+5%=13%

Can anyone please explain this?

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# Homework Help: The approx. uncertainty in r

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