# A copper penny has a mass of 3.1 g and a volume of .35 cm^3. What is the density of copper?

$\rho = \frac{3.1 \cdot g}{0.35 \cdot c {m}^{3}} \cong 9 \cdot g \cdot c {m}^{-} 3$
$\text{Density}$ $=$ $\text{Mass"/"Volume}$ by definition.
Now this is the density of the copper coin, not copper. In the UK copper coins, the $1$ $p$ and $2$ $p$ coins are copper plated steel; clearly, this is done for durability. AS you probably know, pure copper is fairly soft and malleable.