We use the formula,
[tex]m = V \times \rho[/tex].
Here, m is mass, V is the volume and [tex]\rho[/tex] is density.
We can also write above equation as,
[tex]m = \pi r ^2 t \times \rho[/tex].
Here, [tex]V = \pi r ^2 t[/tex], t is thickness circular plate of copper.
Given [tex]m = 71.4 kg = 7.14 \times 10^4 \ g[/tex] and [tex]r = 0.379 m = 37 .9 cm[/tex].
The density of copper = 8.94 g/ cm³.
Substituting these values in above formula we get,
[tex]7.14 \times 10^4 \ g = 3.14 \times (37 .9 cm)^2 \times t \times 8.94 \ g/ cm^3 \\\\ t = \frac{7.14 \times 10^4 \ g}{ 4.0 \times 10^4 g / cm} \\\\\ = 1.78 \ cm = 1.78 \times 10^{-2} m[/tex].
Thus, the thickness of the plate is 0.0178 m.
