1. The standard kilogram (Fig. 1.1a) is a platinum–iridium cylinder 39.0 mm in height and 39.0 mm in diameter. What is the density of the material?

`V=πr^2h`, `ρ=m/V`
Density: `ρ =2.15 times 10^4 kg//m^3`
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Knowns: `m=1 kg` `h=39.0mm =3.90 times 10^(-2) m` `d=39.0mm = 3.90 times 10^(-2) m` Radius of the cylinder: `r=d/2` Volume of the cylinder: `V=πr^2h =π(d/2)^2h` Density of the cylinder: `ρ=m/V` `=m/(π(d/2)^2h)` `=(1kg)/(π(3.90/2 times 10^(-2))^2(3.90 times 10^(-2)))` `=2.15 times 10^4 kg//m^3`