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Old Sep 21st 2019, 06:35 PM   #1
Physics
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Question I've been trying to get the right answer but it doesn't work!

This problem is from Chemistry and Chemical Reactivity, 8th Edition.

A spool of copper wire has a mass of 4.26 kg. How long is the wire in the spool if the wire has a diameter of 2.2 mm? (The density of copper is 8.96 g/cm^3.

The answer is 130 m, but I keep getting 1.2*10^2 m. Am I doing something wrong, or is there something wrong with the book?

Here is my work (some parts may be wrong because I am typing what I wrote on paper):

? g = 4.26 kg * 1000 g / 1 kg = 4.26*10^3 g
? g/m^3 = 8.96 g/cm^3 * 9*10^6 g/m^3 / 1 g/cm^3 = 8.96*10^6 g/m^3
V = m/D = 4.26*10^3 g / 8.96*10^6 g/m^3 = 4.75*10^-4 m^3
?m = 2.2mm * .001 m / 1 mm = 2.2*10^-3 m
r = d/2 = 2.2*10^-3 m / 2 = 1.1*10^-3 m
h = V/πr^2 = 4.75*10^-4 m^3 / ((1.1*10^-3)^2)π m^2 = 1.2*10^2 m
(The answer before applying 2 significant figures is around 125.)

Last edited by Physics; Sep 21st 2019 at 10:06 PM. Reason: Meant to say diameter is 2.2 mm, not 4.2 mm
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