Answer
The edge length of the copper cube is $2.135 cm$
Work Step by Step
We are told the mass of the copper cube is 87.2 grams and the density of the cube is 8.96 g/cm^3. Using the formula for density; $Density =\frac{Mass}{Volume}$, we can solve for the volume of the cube; $Volume =\frac{Mass}{Desnity} = \frac{87.2 g}{8.96 g/cm^3} = 9.732142857 cm^{3}$. Now to find the edge length of the cube we can simply take the cube root of the volume since the volume of a cube is the edge length cubed, so;
$\sqrt[3] {9.732142857 cm^{3}} = 2.135 cm$
